How to know when a competitor drops their price
There are only two reliable ways to know when a competitor drops their price: check their listing yourself on a fixed schedule, or have software check it for you and tell you when the number changes. Checking manually is free and works if you track a handful of competitors and actually keep the schedule. Automated tracking costs money — Shelfhawk starts at $39/mo — and holds up at a bigger scale, because the checks run every day whether you remember or not, and every change is logged with the old price, the new price and the percentage change.
Everything else — noticing your sales dip, spotting the change while browsing, a customer asking why you're more expensive — tells you after the drop has already cost you. The rest of this guide covers the free methods first, honestly, and then what automated tracking should do if you outgrow them.
Why sellers find out too late
A competitor's price drop is public information displayed to everyone except you. Buyers comparing listings see it immediately. Marketplace ranking systems react too: eBay's Best Match and Amazon's featured-offer logic both weigh price, so a cheaper rival tends to surface higher and convert better within days. Shopify stores feel it through Google Shopping, where the rival's price sits directly in the ad unit next to yours.
Meanwhile, no marketplace notifies sellers about rival price changes. The platforms are built to alert buyers about deals, not sellers about competition. So the default way sellers 'find out' is the slowest possible channel: their own sales numbers, which take days or weeks to move visibly and never explain why.
Free method 1: the bookmark folder ritual
Put every competitor listing in one browser bookmark folder. On a schedule — every Monday morning is the common version — open the whole folder in tabs and walk through it, writing each price down. It costs nothing and takes a few minutes per competitor.
Where it breaks: the ritual depends entirely on writing the numbers down every single time. Skip the writing and you're relying on memory — 'was this $24 or $26 last week?' — which turns real moves into shrugs. Skip a week and any move inside it is invisible. And the ritual only sees the moment you check: a drop on Tuesday that's reversed by Sunday never existed as far as a Monday check is concerned.
Free method 2: shopper price-drop extensions
Browser extensions and price-watch tools built for shoppers will email you when a product they track gets cheaper. Some sellers point them at rival listings, and for one competitor on a well-supported site this can genuinely work.
Where it breaks: these tools are built for buyers hunting deals, not sellers watching competition. Coverage skews to large retailers rather than an individual marketplace seller or a rival's standalone store. Alert thresholds are tuned to 'is this a deal worth buying', so a small-but-strategic move — the fifty-cent undercut that shifts a ranking — may never fire. And you get a notification, not a record: no old-versus-new history, nothing you can review across ten rivals at once.
Free method 3: spreadsheet plus calendar
The most disciplined free version: a spreadsheet with one row per rival listing and one column per check date, plus a recurring calendar reminder to fill it in. This one actually produces history — you can see the trend line, and a cell that changed since the last check is unmissable.
Where it breaks: it scales with your patience, not your catalog. Ten listings is a fifteen-minute chore; forty is an hour, twice a week if you want to catch moves inside the same week. It has the same between-checks blindness as the bookmark ritual. And the reminder is easiest to dismiss during exactly the busy seasons when rivals move most.
What automated tracking should do
When the free methods stop fitting, the job description for a price tracker is short. It should check every tracked listing at least once a day — twice if your rivals move fast. It should keep the noise down, because a tracker that cries wolf gets its emails skimmed and then ignored. Every change should show the old price, the new price, and the percentage change, so you can judge severity without opening the listing. And it should keep the history, so 'has this rival done this before' is a lookup rather than a memory exercise.
How Shelfhawk does it
You paste competitor listing URLs — eBay items, product pages on a rival's Shopify store (including brand sites that run on Shopify), and Amazon listings for price and stock. Shelfhawk checks each one once a day on Watch and twice a day on Watch + Suggest and Command. When a price changes, it's logged in your alerts with the old price, the new price and the percentage move; everything that changed since your last briefing lands in a single plain-language email at the time of day you choose, rather than a stream of pings. For the few listings that matter most, you can turn on an instant price alert, which emails you after the check that spots the move. Plans start at $39/mo with tracked-listing caps by tier — details on the pricing page.
If you sell on a specific marketplace, the segment pages show what the watch covers there: eBay sellers get price and stock through eBay's official API, and Shopify sellers can push a recommended price to their own store. Either way, the answer to 'how do I know when a competitor drops their price' stops being 'eventually, from my own sales report' and becomes 'within a day, with the old price, the new price, and the size of the move.'