The floor and the ceiling are the two most important settings in the Buy Box repricer, and the ones merchants most often get wrong. Together they define the band of prices the repricer may work within. It will never set a price outside that band, no matter what a competitor does.
Price floor (min) % and Price ceiling (max) % are percentages of the Shopify price of the variant. They are not fixed currency amounts.
This is deliberate, and it is the single fact to take away from this article. Because the band is a percentage, it moves automatically whenever you reprice in Shopify. Put a product on sale in your store and its Amazon floor and ceiling both come down with it. Raise your store price and the band rises. You never have to revisit the Repricer screen after a Shopify price change. Your Shopify price is the anchor, and the band follows it.
Take a product priced at 40.00 in Shopify, with the default settings: a floor of 85% and a ceiling of 100%.
Assume you do not currently hold the Buy Box, because if you did the repricer would simply hold your price and stop. Assume also that the strategy is Beat the lowest offer with Undercut by set to 0.01. Three situations can arise.
The lowest competing offer is above the band, say 45.00. The target is 44.99, which is above the ceiling, so it is clamped down to 40.00. You are priced at your store price, as high as the repricer is ever allowed to go. You do not follow a competitor upward into high price territory.
The lowest competing offer is inside the band, say 37.50. The target is 37.49, which sits comfortably between 34.00 and 40.00. No clamping is needed and 37.49 is pushed to Amazon. This is the normal, healthy case: the repricer undercuts the competition and stays profitable.
The lowest competing offer is below the floor, say 30.00. The target is 29.99, below your floor of 34.00, so it is clamped up to 34.00. You probably will not win the Buy Box against a 30.00 offer, and that is the correct outcome, because you told the app that 34.00 is as low as you are willing to go. This run counts towards hit the floor in the last-run summary.
A ceiling of 100% means "never price above my Shopify price on Amazon". Two things follow from that.
First, it keeps your Amazon price at or below your own store price. Customers who compare the two do not find your store more expensive than Amazon, which protects your direct channel and keeps the savings line in the storefront Amazon Price block honest.
Second, it protects you from Amazon's high-price suppression. The Marketplace Fair Pricing Policy treats prices significantly above recent prices offered on or off Amazon as unfair, and suppressed listings lose the Buy Box or disappear from the page entirely. Since your Shopify price is a real, publicly offered price, staying at or below it is a safe place to be.
The app constrains the two fields:
A ceiling above 100% permits the repricer to price your Amazon listing higher than your Shopify price, up to twice it at 200%. Amazon's referral and fulfilment fees eat into every sale, so some merchants deliberately list on Amazon at a premium to preserve the same net margin. If that is you, set the ceiling to whatever percentage covers your Amazon fees, for example 115%.
Be aware of the trade-off. The higher the ceiling, the further the repricer can drift above your public store price, and the closer you get to Amazon's high-price suppression threshold. Raise it consciously and not by much. If you are unsure, leave it at 100.
Keep the floor below the ceiling. A floor of 100 with a ceiling of 100 pins the Amazon price to exactly your Shopify price, which is valid but effectively turns the repricer off.
hit the floor in the last-run summary counts the listings where the target price came out below your floor and was clamped up to it. It is not an error, and nothing has gone wrong.
It is telling you that competitors are undercutting you below the price you said you were willing to accept. A count near zero means your floor sits comfortably below the competitive market and rarely binds. A high count, especially on the same products run after run, means one of three things: your Shopify prices are high for that market, your floor percentage is too conservative, or those products need a per-product override because a store-wide percentage does not fit their economics.
Check your margin before you react. The Margin report in Analytics shows price minus Amazon fees minus your Shopify unit cost, which tells you whether there is genuinely room to lower a floor or whether you are already close to break even.