Interesting stuff - there's no right moral answer (and I was neither party to this situation).
Of course, the legal answer is about as black and white as they come - the games were sold even if they were "mate's rates".
What prompted the sale was the expectation that comes along with the "I really want those games" - so the seller passes on his bargain pick-ups to someone that he believes genuinely wants to keep them.
I know I would not feel good about telling another collector that they were games I really wanted, then flipping them for a profit, without at least mentioning it to the original buyer and seeing his reaction.
I guess the amount of time plays a big part - five years down the track, its a whole different market as someone mentioned. But if it was a year or less, the question of what is "right" looms I feel.