You are not allowed to sell a headphone for more than how much it cost to obtain them. Not including shipping, fees, etc.
The only exception are rare and discontinued headphones that are almost impossible to find.
It does not matter about personal opinion, this is simply the rule. It's always been this way on Head-Fi.
I think I'd rather prefer the obvious flip attempts over crafty sellers who fish for best offers. Good intentions or bad, best offer is almost always...