Hi guys I'm buying a flashed Xbox 360 and the guy who I'm buying it off said I can play online.. (is this true) and is there a risk of me being banned..
Yes you can play online. There's always a risk of being banned. Just play it safe, verify your backups with ABGX, don't play early. Don't brag and all should be fine. No promise though.
Double check with him that it is in fact flashed with lt 3.0 Also, as said before, whenever you burn a game, make sure you stealth patch it.
When burning the games, ensure he's using the correct burner for the correct format of the game. For example: XGD3 - iHas burner If he's truncating them, chances are you're more prone to getting banned.