Quoted from grantopia:

I'm sure everyone has their own definition, for me it's more "you know it when you see it". In our area there are 2-3 guys that regularly post WTB ads up and (presumably) flag all the others, which I'm sure in turn gets people flagging theirs. These are the people that seem to be able to drop everything and drive anywhere to scoop up anything resembling a deal the minute its posted. You'll send a message or call on an ad in the first half hour and get "sorry it's sold" and think to yourself "well that has to be Mr. X Y or Z since it's 2:15pm on a Tuesday". Sure enough, the game will pop up on Facebook or the sales apps about 2 hours later for 3-4 times the "deal" price. That's my definition of the "flippers" I was talking about.
I don't assume some moral high ground (especially as a guy who has scored a few killer deals this year), I wish I had the free time and money these people seem to have, and it's their prerogative to spend both how they see fit, and at the end of the day they got there first with the cash. It's more just a bummer to see games I or others would actually want to keep and enjoy for a while being scooped up cheap (which again, good on em, wish it was me) then being sold within hours for a quick profit. I'm not opposed to anyone making money on games or even flipping them really - more just giving my take to the OP that those types of people in the hobby are going to be the ones flagging his ad 99% of the time.