How to Beat AI Price Tests in Grocery Delivery with a 3‑Cart Comparison Rule

Grocery delivery has a new annoyance: “same cart, different price.” Not because you made different choices—but because platforms can run algorithmic pricing experiments, including A/B-style tests, that show multiple simultaneous prices for identical items across shoppers. A 2025 controlled test (437 shoppers) found that about 74% of tested items showed multiple simultaneous prices, with an average low-to-high spread around 13% and highs up to about 23%; identical basket totals varied about 7% on average. The study also reported that demographics and shopping history weren’t statistically meaningful predictors in their sample. (Groundwork Collaborative — “Same Cart, Different Price”)

That creates a budgeting problem: if price is partly a moving target, “I’ll just buy the usual” stops being a stable plan.

So here’s one rule-of-thumb that’s both defensible and low-drama:

The Rule: 3‑Cart Comparison

Build the same cart in three places, then buy the lowest “out-the-door” total.

Think of it like triangulation. If one reading is weird, two others reveal it.

The one formula to remember

T = S + F

T = total you actually pay (“out the door”)
S = item subtotal (including item-level markups)
F = all platform fees you can see before checkout (delivery/service/other required fees)

Then: build 3 identical carts and choose the lowest T.

Why this works (and what it does not do):

It does protect you from “pricing roulette” by making price variance visible in real time. (Groundwork)
It does not rely on folklore “hacks” like incognito mode consistently forcing a lowest personalized price; the provided sources don’t support that as a reliable consumer-safe method. (FTC press release, Jan 2025)

What “AI price tests” look like (in plain terms)

You don’t need to prove motive. You only need to accept the environment:

Prices and promotions can be influenced by data and context, in ways that reduce transparency. (FTC surveillance pricing hub; FTC press release, Jan 2025)
Online grocery totals depend on more than items: delivery/service fees can vary by order, location, cart contents, and membership status—so the cheapest subtotal can lose after fees. (Instacart Help — fees and taxes)
Some services describe different pricing rules depending on membership (including “no markups” claims with exceptions). (Shipt pricing; How are your prices determined?)

This is exactly the kind of messy system where a good default beats endless optimization.

How to run the 3‑Cart rule (fast, not fussy)

Step 1: Choose your three “channels”

The sources support treating different apps and retailer paths as distinct channels because pricing policies differ and can change:

A delivery marketplace (example context: Instacart testing). (Groundwork)
A different delivery service or retailer program where membership status may change markups. (Shipt pricing)
A retailer’s own site/app can behave as its own channel; for example, Walmart’s policy states store purchases can match Walmart.com for identical items (with restrictions), while Walmart.com does not price match to stores/competitors. That’s a reminder: app vs store vs competitor are not interchangeable. (Walmart corporate policy)

You’re not trying to find the “best” platform forever. You’re finding the best today for this cart.

Step 2: Make the carts identical

Identical means:

Same items, same sizes, same quantities.
Don’t let substitutions silently change the comparison.

If you can’t match perfectly (one channel lacks an item), use a “core basket” of identical staples for the comparison and treat the missing items separately.

Step 3: Compare out-the-door total, not just items

Platforms explain that fees vary and are part of what you pay; in Instacart’s help guidance, service fees can vary, and the final total depends on multiple components. (Instacart Help — fees and taxes)

So compare what you can see right before checkout:

Item subtotal (S)
Delivery fee (if any)
Service fee (if any)
Any other required fees shown

Then pick the lowest T = S + F.

Step 4: Use pickup as your baseline (safer variant)

The 2025 controlled experiment used pickup to reduce delivery-cost confounding—and Instacart states pickup orders don’t have service fees. That makes pickup a clean way to see item-price behavior without some fee noise. (Groundwork; Instacart Help — fees and taxes)

Safer variant:

Run the 3-cart comparison in pickup mode first.
If you truly need delivery, re-check delivery totals after you’ve identified the item-price “winner.”

This protects you from confusing “cheap items, expensive delivery” vs “expensive items, cheap delivery.”

Pocket Card: The 3‑Cart Comparison Rule

Rule: Build the same cart in 3 channels. Buy the lowest T = S + F.
Use when: You’re doing online grocery where fees/markups vary or you suspect “same cart, different price.” (Groundwork)
Don’t use when: You must place a time-critical order and can’t confirm totals; or items aren’t comparable across channels (different sizes/brands only).
How to adapt: Use pickup to baseline item prices first. Include membership status as a variable. Re-check totals near checkout to catch fee tiers. (Instacart Help; Shipt pricing)

Worked mini-scenarios (no currency, just structure)

Scenario 1: “The cheapest subtotal loses after fees”

You compare three identical carts:

Cart A: S = 1.00 (normalized), F = 0.12 → T = 1.12
Cart B: S = 1.04, F = 0.04 → T = 1.08
Cart C: S = 1.01, F = 0.09 → T = 1.10

Winner: Cart B, even though its items cost more.

This is why the sources emphasize comparing out-the-door totals: fees vary by multiple factors, and focusing only on the item list can be misleading. (Instacart Help — fees and taxes)

Failure mode: You optimize S and ignore F.
Fix: Always compute T right before checkout.

Scenario 2: Fee thresholds (the “cliff” problem)

Some platforms introduce tiered fees below a high order-size cutoff (reported for Amazon Fresh), meaning a cart near a threshold can flip winners depending on whether it falls just above or just below the cutoff. (CNBC; AP News)

Model it as:

If S < θ, then F = f_high
If S ≥ θ, then F = f_low

Two carts with almost identical items can land on opposite sides of θ due to small differences (availability, substitution, channel-specific pricing policy). The result can look like “randomness,” but it’s actually a threshold cliff.

What the 3-cart rule does here: it forces you to see whether the “winner” is genuinely cheaper or just dodging a fee tier.

Failure mode: You declare a winner without checking whether you’re near a cutoff.
Fix: If you’re close to a threshold, compare both versions intentionally: one just under, one just over—then pick the lower T.

Scenario 3: “Pricing roulette” and spread risk

The 2025 controlled test found simultaneous price differences for identical items across shoppers and meaningful basket-total variation even when the cart is the same. (Groundwork)

Treat the spread like a risk band:

If you observe a typical spread p between low and high, then your “overpay risk” is roughly p when you don’t compare.

You don’t need to predict why you got the high. The study’s sample didn’t find demographics/shopping history as statistically meaningful predictors, so trying to reverse-engineer “what the algorithm wants” is a bad use of your time. (Groundwork)

Failure mode: You try to outsmart personalization with gimmicks.
Fix: Compare multiple carts in real time; it’s the strategy the evidence supports.

Edge cases and where the rule breaks

1) Membership status changes the game

Shipt states that some users may see slight markups vs in-store to cover costs, and that Target Circle 360 members generally see “no markups” (with exceptions such as alcohol). That means membership status can be a pricing variable, so it must be held constant during comparisons. (Shipt pricing; How are your prices determined?)

Rule tweak: Compare as you actually are: same membership status, same logged-in state across channels.

Also note: Instacart’s minimum order/subscription dynamics have shifted, with reported behavior changes when minimums changed—so any “membership math” should be re-evaluated when policies move. (Investopedia)

2) “No surge” claims don’t remove the need to compare

Shipt explicitly says it does not charge surge/busy pricing. That’s useful, but it doesn’t eliminate other drivers of total-cost differences (markups, fees, membership rules, item pricing). (Shipt surge/busy pricing)

Interpretation: Even if a service denies surge pricing, the total can still vary across channels—so the 3-cart rule still earns its keep.

3) “Price parity” labels help, but don’t replace checking

Instacart’s response to the 2025 report emphasizes price parity efforts, that retailers control pricing, and that pricing policies are displayed on storefronts to help customers compare. Use that as a prompt to look for the policy label, but still run the numbers. (Instacart company update)

Rule tweak: Treat policy labels as metadata; treat T as truth.

4) You can’t always build perfectly identical carts

When one channel lacks an item or only offers a different size:

Either swap all channels to the same size/brand,
Or split the comparison into two parts: “comparable core” vs “non-comparable extras.”

The rule is about controlling what you can control.

Minimal budgeting tie-in (without app mechanics)

If you track spending in Monee (or anywhere), the clean mapping is:

Put items and platform fees in separate labels/categories so your budget reflects S vs F.
Set a simple cap like delivery+service fees ≤ X% of grocery items per pay cycle; if you consistently exceed it, switch more orders to pickup as the default baseline. (Pickup has fewer fee components in the Instacart policy description.) (Instacart Help)

That’s it—no elaborate system required.

What’s not proven (and why that’s freeing)

The sources don’t provide a reliable, repeatable “hack” to force the lowest individualized price (cookie tricks, incognito, constant account resets). What they do support is that individualized and contextual pricing can exist, and that it can be opaque—so transparent comparison shopping is the defensible countermeasure. (FTC press release, Jan 2025; Groundwork)

The emotional win: you stop negotiating with a black box. You just compare three readings and move on.

A clean checklist (the “do this, then stop” version)

Build 3 identical carts across 3 channels.
Start with pickup when possible to baseline item-price behavior and reduce fee noise. (Groundwork; Instacart Help)
Compare out-the-door T = S + F right before checkout. (Instacart Help)
If you’re near a platform threshold, assume a cliff exists and compare intentionally. (CNBC; AP News)
Keep membership status consistent across carts. (Shipt pricing)
Buy the winner. Don’t overthink it.

Educational note: This is general information, not individualized financial advice. Policies and totals vary by location, retailer, membership, and time; always confirm your own checkout totals.