Be like the little engine that could, and keep pushing along. It will take time, but the time you take will be worth it. If you see an offer in the mail that is far too good to be true, it probably IS too good to be true. Don't fall for the get rich quick junk, and don't try to sell the stuff, either. Your customers won't be very loyal after you burn them.
Customer service is of the utmost importance in mail order.
Give a good guarantee on your products. If they are good and deliver on your advertised promises, you won't have to worry about many customer returns. If a customer has a complaint, make sure you answer them quickly and kindly. Sometimes, the best return customers are the ones who have had problems that you've corrected. They see that you have their interests in mind, and respect you for that.