Likewise, be careful buying a bike off a mate.
I bought a CG125 off a mate, its exhaust was rotted and chain was shagged, so I replaced both with new items, replaced all the engine bolts with stainless hex bolts, passed my test on it and then sold it for more than I bought it from my mate for. I made the mistake of telling him how much I sold the bike for and he thought I had ripped him off when buying it even though I had spent a couple of hundred in the intervening time which I didn't get back.