Me and my friends have only bought off a street dealer one time, was after a music festival.. we were calling people too try get some anyway, guy comes up and asks if we wanted to buy any, it felt too convenient... but he was cool and we knocked his price down a bit.
I prefer to go through people i know though.. for any drug.
I've had random people ask me for drugs, i dunno why.. maybe i look like a dealer.. but i just tell them 'nah, got none' even if i do lol.