Technically, one must be physically present in the country where they applied for the eVisa. Of course one can cheat the system, but it will be immigration fraud, and if caught, the penalty can be up to 5 years of imprisonment and up to a fine of 10,000 baht. Each time you enter, you get 180 days to stay. The visa is valid for five years from the day it was issued (not when you entered Thailand).
looks like anonymous has not visited any country except Thailand. Hence, he is confused about exit stamps just like Tom the brick layer, Dick the carpenter and Harry the truck driver.
If you are trying to get Thai clients, it is not allowed. If you are talking about clients outside Thailand, then I would suggest you move to your home country, why you need a DTV visa?