It's bizarre that your question has gone unanswered for this long, even though it's more about how PayPal works rather than how Payment Form works.
I registered for PayPal years ago intending to be a seller and PP insisted on having a checking account number and routing number to sign up; even worse since they could make deposits or collect fees, they could freeze the entire account. I went to the trouble of opening an account just to use with PP.
Today when someone attempts to use PP for the first time (i.e. from an email address that PP doesn't recognize) they offer to let you use a credit card instantly. If you look in the fine print, you are actually creating a PP account. If you use this account several times, PP will "suggest" that you "verify" your account with a bank and routing number.
Once you have given them a bank number, they will always take any payments from the bank first and only use the credit card if you say to do so specifically, each and every time. They prefer banks because they get the money instantly.
If you want to be paid through PP, you must have a bank. They will not take a payment and send it to your credit card as a "deposit". Also, when you are paid, the money sits in a holding mode with PP. You have to ask to have it transferred to your bank. Typically, that takes about three days. I don't think they automatically transfer, you must ask.
The goal here is for PP to collect quickly and payout slowly. If you send money, they pay "instantly" - meaning it goes into someone else's hold. They may allow anyone to have "hold" money and then wait for a check request, I don't know. PP is good in that your vendor knows you've paid and can ship or provide service immediately. The actually transfer of money to him takes a few days and is subject to limitations. Oh yes, they also collect a fee out of what you pay.
If you use Payment Form to accept PayPal payments, I think it assumes you already have an account. Also, this has to be enabled in a less than obvious way. It does work though, I'm using it for a non-profit organization. Go to PP and check the fees, it's something like $.75 plus 2% - on an $80 fee we net $77.38. I then transfer the money from PP and once my bank has it, I pay the club. (Actually I move it electronically from bank A to bank B and from bank B to the club account bank C. Only bank B allows me to do this electronically and without fee - but it takes two steps and 3 days to clear, twice.)
Dave Sause
oldandfat@cox.net