Oh yeah, we've had guys, more than once, make it very clear they're keeping track of our listings with messages like 'you've had this up for three weeks, maybe just sell it to me for X.' My favorite is coming back with 'I actually didn't want to sit on it for a week and I didn't want to sell it for an insulting amount, so I gave it away and forgot to take the listing down.' I've even had people accuse me (or my wife) of LYING about not having the item anymore because 'no one just gets rid of things for free.'