Street traders are great material - this sort of thing really sharpens your people photography skills no end.
Steer clear of the coward's way of using a telephoto. Get a wide angle on and get in close. Ask if you can take the phot and don't forget to talk to the subject as you work.
Also don't be afraid of asking them to turn a head or alter their stance to improve a shot. And don't 'shoot and scoot' - hang around and shoot a whole series once you've found a willing and photogenic subject.
Try for a series of shots that tells a story about one character rather than blasting away at a whole load of different people. Or, if it's a market, get along early and start with them setting up. Then shoot them throughout the day and end with the clearing up - get a series of shots that encapsulates the feeling of the whole market.
That way they'll know that you're not just a tourist with a camera, but a 'serious' documentary photographer.
Some may be dole-bludgers, so reassure those that don't want their photos taken that they'll not be shown to the authorities.
In fact I'm off work on thursday, so I'll do some at the covered market in town.
We can compare notes.