Flipagent

flipagent tells you on the eBay page itself whether a listing is
statistically worth flipping.

A chip appears next to each item's price on search results. Click
it to get an estimated net profit if you bought at the listed price
and resold, built from:

• Recent sold history: median, distribution, sell-through,
days-to-sell
• Currently active listings: how much supply is competing and at
what prices
• eBay fees, shipping, and your cost basis subtracted out

On the item page, the same estimate expands into a full breakdown:
sold comp set, active comp set, suggested resale price band,
projected margin range.

Why install it:

• The math runs the second you see a listing, not after you've
bought it.
• The estimate appears where you're already shopping. No
dashboard, no copy-pasting item ids.
• Evaluate from search, then open the item page. Same estimate,
no re-run, no double credits.

You'll need a flipagent account and an API key. Free tier at
https://flipagent.dev. The extension reads listing prices and runs
evaluations against your account. It never stores your eBay
password and never completes checkout for you.