@Suntan12 - I think that it is best to buy a mail order business that is for sale because this way you avoid the common pitfalls of early entrepreneurship and will not fall prey to many of the scams out there.
You can go to a business broker who helps people buy and sell businesses just like how a real estate agent or broker helps people buy and sell homes. They can find you the right mail order business opportunities for you.
You can also see the actual income that an existing internet mail order business brings in to give you the idea of what to expect. The business broker does not charge for the consultation. They make their money from the sellers not the buyers.