A tuk-tuk driver will offer his services for a day sometimes for as low as 50 cents if you agree to go inside of three shops throughout the course of the day. In exchange, fuel coupons will be provided to driver by the shopkeeper. Technically, you do not have to purchase anything, but each shop -- usually a tailor, a jewelry shop, and a souvenir shop -- will rake on the pressure in an effort to recoup the cost of the fuel coupons.
Do yourself a favor: by Is not agreed to gone in the shop to avoid one of Thailand's oldest tuk-tuk scams.