A buddy of mine and I did it for a while in university. We had a friend with an account at a computer parts wholesaler. We bought each of us a system for cheap. Then, we listed one in the classified ads section as being for sale. People would call about it, and we'd end up telling them they could get whatever they wanted from us, and that we could basically give them the same price as any local computer store, but without the taxes (14% at the time). We'd recommend a setup, they'd okay it, we'd order the parts, I'd assemble it, they'd pick it up, and we'd cash our cheque for the cost plus our profit (we'd make about $250 on a $2000 computer sale). Then, we'd go blow it all at the bar. It rocked.
The lady at the bank gave us the weirdest look in the world when we said we wanted to open up a joint chequing account though... hehe.