The problem here isn't the chips themselves, it's trading practices.
Let's be honest - for the prices we pay for this sort of stuff, we can't expect anything other than recycled old parts. That's risky, but all part of the game when working with things that have been out of production for decades. I fully agree with the practical recommendation to buy a chip (or two) extra. Most work, most will probably still work years down the line, but there will be dodgy units. And I don't care so long as the seller is honest about it being untested too. If someone goes to the trouble of testing a part, the value increases sharply - but that also opens up a whole new world of fuss and bother with returns if it turns out not to work (or the buyer messed up his board and blames the chip...). In general I'd say the eBay sellers are pretty decent about it, I've even had a seller replacing a dead chip that wasn't even marked as tested (Commodore SID) and at worst they just don't care about where stuff comes from. It's further up the chain that the nasty stuff happens. The only time I'd contemplate giving the sellers a hard time is if they put up a pic of a legit chip and you get fakes, or if they advertise NOS and stuff is obviously used and faulty too. If the pic itself shows nice 2015-marked 1980's chip, you're just getting what you ordered. Caveat emptor.
So what do I do if I get one for one of my projects? Tbh, I try it out and if it works as desired, I'm happy enough, unless I paid over the odds for something very specific.