There are some issues with using paypal in place of a merchant account with a bank. It is not nearly as safe, or as stable, and you really have no control over it. Most larger business don't accept paypay for these reasons, as well as because it's too easy for the person submitting the payment to cancel it on their end.
Having said that - it's cheap, it's easy, and it generally works. Most smaller start ups and individuals don't need the hassle of opening a merchant account.
That's pretty much the opinion that get from Merchants who have been at it for a while. From what I hear, Paypal is all about backing up the customer, but not the merchant. My biggest recommendation to CYA is to see if their set up has a "charge automatically" option. It helps a little with the cancellations.