FlipperHelper - From car boot to eBay — track every flip's real profit

Hey Product Hunt. I'm Oleksandr, a backend developer based in London. I built FlipperHelper because my wife asked me to. Last summer she came back from a car boot sale with a car full of furniture and no idea what she'd paid for half of it. She buys at car boot sales and charity shops, then resells on eBay, Vinted, and Facebook Marketplace. Margins are decent — that's not the problem. The problem is remembering what you paid for a side table three weeks ago when someone messages with an offer, and which platform that lamp is actually listed on. She was running the whole thing from memory. The other constraint: most car boot sale fields in the UK have zero phone signal. So whatever I built had to work in a field with no bars. FlipperHelper is what came out of that. Free, no item cap, no ads, no subscription. Works fully offline. Tracks listings across 16 selling platforms. Calculates real profit after every expense (entry fees, transport, packaging, platform fees) — not just gross sales. Has a feature called Hauls that groups items and expenses by sourcing trip, so you can see whether last Sunday's car boot run paid for itself across all the items as they sell. The honest numbers: 81 first-time downloads in 90 days, 29% App Store page-to-download conversion, mostly UK resellers. Real users have been the source of half my feature ideas — Hauls itself came from a Reddit comment. I'd love feedback on whether the reselling-specific framing lands, or if I should position it more as a generic inventory + profit tracker. The reseller niche is small but high-intent; the broader inventory market is enormous but harder to differentiate in. Happy to answer anything technical, marketing, or product. Took 43 days to build version one, mostly in the evenings, with my wife as the only beta tester.