I recently tried integrating PayPal’s APIs with a site I work on and I jumped the gun before reading (I know, rookie mistake). I had integrated many other payment processing systems and I assumed wrongly that PayPal would accept test credit card numbers for testing. They flagged this as fraud, which I suppose is valid, and locked my account, limiting my ability to finalize my site.
They gave me a list of things to do to reinstate my account, and I did them, then they got more aggressive and asked for more validation, specifically the billing details that matched my credit card number—a test number that I obviously couldn’t provide. I explained this to them and they reinstated my account. I had little hope up to this point due to PayPal’s bad PR lately, but they solved my problem with a minimum of fuss, though it did take a while. Score one for the good guys.