first time i was asked was actually by dave ^^ *E7*, he rolled up and politely asked "has anybody ever offered to buy your car"
second time was a car full of irish lads, "hey nice corolla, sell it to me" that was a bit freaky because they kept on asking..."come on...come on sell it"
third was a bogan chick in a commodore, wound down her window, made what i could best describe as a bong symbol with her hand and said "hey mate wanna sell your car"