I don't often buy from them, but not because I think their produce is no good or their prices are too high (to be honest, I couldn't tell you how their prices compare to those of the supermarkets). It's really just a personal preference - because of the way my mind works, I find it easier to buy all my groceries in one place. Perhaps I should make a little pact with myself to buy something from the next roadside fruit-seller I see, just for the experience. :-)
One thing I do know, from being invited to buy their products when I'm stopped at the traffic lights, is that the first price they quote you is very seldom the price they actually expect you to pay. Most times, when I indicate that I don't want to buy, they'll immediately drop their price, saying something like, "Today, just for you, I'll make it TWO for [insert original price here]." So next time I think I'll take them up on that Special Deal that's Just For Me and Only For Today. ;-)