The ability to accept payment via credit card is important if you're looking to build an information marketing business. You can certainly get started with only PayPal but long term you will limit your growth somewhat by not taking the major credit cards for payment.
Visa and Mastercard are, of course, the two biggies in this game, but you should probably supplement them with American Express and, in most cases, Discover. If you were going to rank the four in order of importance to accept most would probably rank them this way:
1. Visa
2. Mastercard
3. American Express
4. Discover
When you are initially setting up your merchant accounts there are three primary questions the merchant account provider will want. First, what types of good will you be selling. Second, what is the size (in dollars) of the average transaction you'll be processing with them? Third, what is the total dollar volume you anticipate running per month?
They will monitor your activity levels and, if something out of the ordinary suddenly appears, it will cause the proverbial "red flag" to be waved. For example, if you do a new product launch where you suddenly run 10 - 20 - 50 times the dollar volume through your account than you normally do you better believe that'll get their attention. And they can shut your account down instantly.
That's why it's so critical to communicate in advance with your merchant account provider and let them know when you're planning a special promotion, or if you're raising your average ticket price, or starting to sell a different type of product then you've sold previously.
Merchant account providers are on constant alert to make sure their potential liability is minimized as much as possible. Most don't take chances period, and if you have a lot of transactions that are outside the parameters set up when you started your account you run the risk of losing your ability to accept credit cards. And, if you're an information marketers, that could be catastrophic to your business.