To compare prices across websites properly, compare what you would actually pay: the item price plus shipping and tax, minus any member price or coupon you qualify for. Comparison sites and extensions mostly show the sticker price from stores that send them data. Sai checks each store you name the way you would, works out the delivered total and sends you a ranked list with links. It does not buy anything.
What it means to compare prices across websites
Comparing prices across websites means finding the same product, in the same model, condition and seller, on several stores, then ranking the stores by the total cost delivered to you. That total includes shipping, tax, membership pricing and coupons, not only the listed price.
Two listings with the same name can still differ. A refurbished unit, a marketplace seller, an older model year or a bundle all change what you get. A fair comparison matches those details first and compares prices second.
Why the cheapest sticker price is often not the cheapest
- Shipping and tax appear late. For most online shopping, you see them only in the cart. The FTC rule on unfair or deceptive fees, in effect since May 12, 2025, requires an up-front total price only for live-event tickets and short-term lodging. Even there, government charges and shipping can be shown separately, as long as they are disclosed before you pay.
- Member prices are behind a login. Club and loyalty prices show only when you are signed in, so tools that read public pages miss them.
- Coupons vary by person. Coupon extensions show the codes available to them. In December 2024, PayPal said that merchants determine which coupons are offered through Honey.
- "Was" prices can mislead. The FTC's Guides Against Deceptive Pricing say a former price is a fair comparison only if the item was genuinely offered at that price on a regular basis. A higher price set just to advertise a discount makes a false bargain.
- Coverage has gaps. Google's free product listings rely on data each merchant submits through Merchant Center, and Google says products are not guaranteed to show. A store that does not submit data, or is not matched, will not appear.
Example: sticker price versus delivered total
An illustrative comparison of one pair of headphones at four stores, shipped to the same ZIP code. The lowest listed price is not the lowest price you pay.
| Store | Listed price | Shipping | Est. tax | Member price or coupon | Delivered total |
|---|---|---|---|---|---|
| Store A | $328.00 | $0.00 | $29.19 | None | $357.19 |
| Store B | $319.00 | $12.99 | $28.39 | None | $360.38 |
| Store C | $348.00 | $0.00 | $27.59 | $38.00 off for members | $337.59 |
| Store D | $329.99 | $0.00 | $26.43 | 10% coupon on the product page | $323.42 |
Store B has the lowest sticker price and the highest delivered total. Store D is cheapest only once its coupon is applied, and Store C beats both A and B only for members.
What to match by product type
| Product type | Details that must match | Costs that hide in the cart |
|---|---|---|
| Electronics | Model number, storage or memory, color, region, new versus refurbished | Shipping speed upgrades, extended warranties added by default |
| Appliances | Model number, finish, fuel or voltage type | Delivery, installation, haul-away of the old unit |
| Furniture | Dimensions, material, color, what is included | Freight or white-glove delivery, assembly |
| Household and groceries | Size and count, so you can compare unit price | Minimum order amounts, membership fees |
| Baby and outdoor gear | Model year, included accessories, safety recall status | Oversize shipping |
A price comparison checklist
Use this for any purchase, whether you check by hand or hand it to Sai:
- Pin down the exact item: model number, color, size, condition (new, open-box, refurbished) and what is in the box.
- Check who sells it: the store itself or a marketplace seller, and that seller's ratings.
- Get the delivered total: add to cart, enter your ZIP code, and read shipping and estimated tax. Stop before payment.
- Look for your own prices: member pricing, store-card discounts, and coupons on the product page.
- Compare the terms: delivery date, return window and who pays return shipping.
- Treat "was" prices with care: rely on a price history you can see, not on the crossed-out number.
Ways to compare prices across websites, compared
| Approach | Stores covered | Shipping and tax | Member prices | Price alerts |
|---|---|---|---|---|
| Manual tabs | Any store you open | Yes, if you go to each cart | Yes, if you sign in | No, you check again yourself |
| Google Shopping and Google price tracking | Merchants whose product data Google shows | Shipping where the merchant provides it | No | Push and email alerts when signed in (US, Canada, Australia, Japan and India) |
| Coupon extensions (Honey) | The store you are on, plus Droplist alerts at partner stores | No | No | Droplist, at partner stores |
| Amazon trackers (Keepa, CamelCamelCamel) | Amazon only | No | No | Yes, with price history charts |
| Sai | Any store you name | Yes, from each cart, for your ZIP code | Yes, after you approve each sign-in | Weekly checks you schedule, alert on a set drop |
If you only shop on Amazon, Keepa or CamelCamelCamel is quicker and adds long price histories. For a fast look at many stores at once, Google Shopping is the better starting point.
How to compare prices across websites with Sai
- Name the item and the stores. Give the exact model, condition, your ZIP code and the stores to check. The full prompt is in the Start with a prompt tab above.
- Let Sai check each store. It searches each site, confirms the model and seller, and adds the item to the cart to read shipping and tax. It stops before any payment step.
- Approve sign-ins for member prices. Sai asks before it signs in to any store account. Credentials are approved through a link, not typed into the chat.
- Review the ranked sheet. Every store, cheapest delivered total first, with the delivery date, return window and a link to the product page.
- Schedule a weekly check. Sai repeats the comparison and emails you only when the cheapest total drops by the amount you set.
Sai ranks #1 on OSWorld, the public benchmark for agents that complete tasks on a real computer. Once Sai completes a task, its steps are kept as code that replays the same way, so the weekly check is faster and more consistent than the first run.
Shopping safely with an agent
- No purchases. For this task Sai only reports prices and links. It never checks out, and it does not complete payment on any task without your approval.
- Carts, not orders. Sai adds items to a cart only to see shipping and tax. You may want to clear the cart afterward.
- Sign-ins on your terms. Approve once, for the whole task, or deny. If you deny, Sai skips that store's member price and says so.
- Personal use only. Check a handful of stores for something you plan to buy. Don't use this to scrape catalogs, monitor stock for resale, or break a store's terms of use.
Related use cases: monitor competitor websites for changes and find and cancel subscriptions you forgot.
Last reviewed October 7, 2026.