The counterfeit/replica market for electronics, especially Apple stuff, has gotten really, really good. You often won't be able to easily tell just from the sealed box if it is a fake or not -- though opening usually offers some clues because the counterfeits often don't have the same attention to detail with the opening tab stickers and whatnot. And the stuff that is often hardest to tell, at least with a cursory glance, are AirPods and AirPods Max headphones.
Because I have some friends who don't listen to me and insist on buying things from Facebook Marketplace, I've seen some very convincing looking AirPods Max headphones (you can tell they are fake because of markings inside the ear cups amongst other things, they also usually feel lower quality but that's hard to judge if you aren't familiar with the real things) that will often pair exactly like legit AirPods because the reps have managed to either clone the H1 chip or reverse-engineer the pairing process. The fakes often have real (stolen) serial numbers on the boxes so if you aren't familiar with how Apple does their plastic sealing and just ran a serial number off the box to see if it was legit through the Apple serial number checker, you'd probably think they were legit until you opened them up.
At this point, I would guess that at least 90% of the "sold as new" AirPods and AirPods Max on eBay are fakes.
This is very different from the old-school world of grey-market cameras sold off of street corners in New York that were often legit but were either fenced and/or from foreign markets without official support/warranty.
The rep handbag game has become incredibly good too, to the point that there is now a subculture of people (some who could even afford the legit offerings) who collect and pay real money for the reps that are largely indistinguishable from the real thing -- but that might cost $800 instead of $18,000.