If you want to sell a product online, you most probably need to consider processing credit card transactions. There are 2 ways you can do that: (1) by having a merchant account, or (2) by using a third party payment processor. If you are small and you have a limited budget and revenue, you better choose a third party payment processor.

Thanks for this information!

Now in my case I need to charge businesses that advertise in a Directory. So it is not a product that we will ship. Does this differ in any aspect? I saw the smallbusiness.yahoo.com merchant solutions and want to try it, but their solutions are based on shipping products etc. Also is there any programming involved if I would want to charge them automatically every month? or does the customer have to pay every month?