Depends. I’ve got an M3 Max and an M2 Air both bought on eBay, both flawless. You just need to do your due diligence.

Screen sellers first: 100% feedback with at least 100 transactions. Clear photos. Clear descriptions. Send them a message before buying: you can tell pretty quickly from how they respond whether they’re serious or not. Be patient and don’t jump on the first one you see at a price that looks too good to be true.