Is MarketHelper free?
Free to start, and free to stay if you sell casually — the free tier covers your first few active listings, which is enough to run real offers through it and see whether the numbers change how you negotiate. If you're selling at volume there's a paid tier for a few dollars a month. No card required to begin.
Does it work on Facebook Marketplace, eBay, and Poshmark?
Yes — and OfferUp, Mercari, Craigslist, or anywhere else you sell. MarketHelper works by copy and paste rather than by integration, so it isn't limited to the platforms that happen to offer an API. Fee assumptions come preset per platform, and you can edit them to match what your account actually gets charged.
Do I need to connect my marketplace accounts?
No. There's no login, no OAuth, no account linking. You paste a message or type a number, and that's the whole setup. MarketHelper never touches your seller account and can't post, message, or act on your behalf — which also means there's nothing to get your account flagged.
Is my data private?
Your listings, floors, and sale history stay on your own device. There's no account to create and nothing is uploaded — the profit math runs locally, so it works with the wifi off. You can export your full history as CSV whenever you want it somewhere else, and delete it in one click.
How is this different from just using a calculator?
A calculator gives you a number — if you already remember the platform's fee structure, your shipping cost, and what you paid for the item, and if you're willing to work all that out at 11pm with a buyer waiting on you. MarketHelper already knows your floor, applies the right fees for the platform you're on, and answers in one glance. It also remembers, which a calculator never does: at the end of the month you can see what you actually made and what you turned down, instead of guessing at both.
Who is this built for?
Resellers who sell across more than one platform and handle enough offers that guessing gets expensive — furniture and electronics flippers, thrift and estate resellers, anyone running a side business out of a garage or a spare room. If you sell one thing a year, you don't need this. If you're fielding lowballs every evening, it pays for itself the first time you hold the line.