If I open the box upside down.. or turn it around to get it out of the packaging material, I'll see the bottom... but not necessarily 'scrutinize' it.. unless there's something else wrong and I'm trying to figure it out.
'Mint' means 'mint' which means no scratches anywhere and very light, if any, usage. If I bought a 'mint' piece of gear and saw little scratches anywhere, I'd think it was 'near mint' condition but not 'mint'.
However, if they were on the bottom, I wouldn't really care. That would definitely make it a 9/10 vs. 10/10, though. If the unit appeared to have been used a fair amount, I'd be a little more aggravated.
If the guy got a really good deal for even an 8/10 player, then I'd tell him where he could shove it. But if he paid a little more and was expecting a perfect piece of gear that looked, worked, and felt like brand new, then he has a reason to quabble... at least a little.