paypal problem when pay with credit card

Hi,
I've posted a few times about problems with Paypal. Certain times, paypal is telling the site the subscriber paid, when they have not, and content is being released. We think we nailed it down to when people are trying to pay with a credit card through Paypal as opposed to have an account already set up. Any insight on this? It's been very bad b/c the client is losing money when these get approved even though payment has not gone through.
thanks!