So, one problem solved.... sorta
On the one that is a gift certificate only - the cart is acting like they have to pay a penny but it never actually takes a penny from PayPal.
On the other hand - the customer is trying to apply a coupon code that has restrictions on some items so it won't apply to the entire sale...and then checkout with a Gift Certificate. This is the problem they just explained to me:
I haven't put anything through yet, but I've been experimenting, and it seems to be tied into Kristy's coupon code. If I use the GC to pay without using the discount code, then on the step 3 page, the payment method is blank, even with multiple items in my cart. But if I use the discount code and the GC, even just for one item, then it shows the payment method as Paypal and I get the same problem as before where it takes me to the Paypal page.
Also, if I enter a balance from the GC that is MORE than the amount owed while using the discount code, it gives me a negative total (which, of course, Paypal doesn't like either), but if I do that without the code, it just brings it down to zero. Apparently, using a GC along with the discount code confuses the cart.