Dear Danielle:
Some time ago you shared that using the credit card authorization form, you go into PayPal and “pay yourself.” Do you log into the client’s account? Forgive me if I seem clueless. –TK
Nothing to forgive. It’s a good question. 
Okay, so the credit card authorization form is an agreement between you and the client whereby the client provides you with their credit card details and allows you to keep them on file so that when their fee to you is due, you can simply run the credit card yourself instead of waiting for them to do it. This is an excellent way to take another detail off of your client’s plate while ensuring you are paid on time every month. My client’s love it and I never pay myself late, lol. 
It’s best for clients who are on retainer or otherwise owe/pay you a standard/set amount on a regular basis. And it really doesn’t matter what credit card processing service you use.
With regard to PayPal specifically, as you ask, there are a couple ways you can process the payment.
The first is that, yes, you can log into the client’s PayPal account if they wish to provide you with that information. However, it’s not necessary and for many reasons I really don’t recommend this. There needs to be a great deal of trust there already for a client to provide you with their PayPal account info and a) that level is usually only established with clients who have been with you for years, and b) you don’t want to get blamed for any problems with their account just because you are the only other person who happens to have access to it. Know what I mean?
I advise the second option, which is that you simply process the payment as a guest. As a guest, you don’t need to log into a client’s PayPal account to process their payment. As long as you have their credit card details and the proper legal authorization form on file, you can process any payment without the client even needing an account. And even if they have an account, you don’t need to log into it.
What I recommend is that you set up a “payment” page on your website. Here’s an example of my payment page from my old website:
Get the HTML code from your PayPal account (found under the Merchant Services tab) and insert a PayPal generic “Pay Now” payment button on that page. Then, whenever you need to process a payment on behalf of a client, you just go to that page of your site, click on the option where it says “Pay with your debit or credit card as a PayPal guest” and then enter the amount due and their credit card information. Simple as that.
Let me know if that helps
