Here's my take on this whole topic.
I've been reselling as a full time job for 3 years now. The emphasis is on videogames, but i do buy and sell other things too.
Just a few points:
-Sonic 1,2,3 + SMB1,2,3 (PAL copies, loose) will cost you the same £45 a new game costs nowadays.
-There is no difference between reselling videogames to any other business on the planet. (ie:please don't single s out as being "fags")
-Collectors collect to collect, i don't know anybody locally or through facebook sites who is collecting games as a kind of investment. There are certainly people out there who do that kind of thing, but i would not call them collectors.
-Emulate, emulate, emulate. If you are poor, or like me, cannot see the point in spending half a monthes rent on a crappy game which just so happens to be rare, then buy a PSP and emulate.
-Buying and selling is becoming alot harder, noticeably this year. Everyone seems to have wisened up due to Facebook buy and sell groups, CEX now selling retro, etc.. I sincerely miss the days of regularly buying stacks of MD games for 50p each.
-I personally think people are retarded to get games graded and then never play them. But it's your money i guess.