If you're buying something locally and meeting the seller in person, you already have the one advantage that no amount of listing photos or seller assurances can replace: you can test the actual device, with your own hands, before any money changes hands. That's worth using deliberately, not just glancing at the item and handing over cash.
Before you go
- Agree on a public, well-lit meeting place — a coffee shop or a busy retail parking lot, not somewhere isolated.
- Ask the seller to have the device charged and ready to power on when you arrive — you want to test it, not watch it boot for the first time in a week.
- If it's a device with a known common failure mode (a console's analog sticks, a camera's zoom lens, a laptop's battery and screen), decide beforehand what you're going to check, so you're not improvising under time pressure.
At the meetup
Power it on. Run through the one or two things that actually tend to fail on that specific device — not a generic glance, the actual check (stick drift on a controller, zoom-and-photograph for a camera, sign-in and network access for a console). Only pay once you've seen it work, not before.
Where this doesn't apply
None of this helps if you're buying something that's shipping to you instead of meeting up — which is now the more common way people buy used electronics, and the one case where you genuinely can't do any of the above yourself before paying. That's a different problem with a different answer (having the seller run the same kind of check on camera, before you commit, is what TestPass is built for) — but if you can meet up in person, you don't need a tool for this. You just need to actually do the check.