Basically, I'm going to cover how you can easily get people back to your website, download page, or any custom link after your customer pays through one of your custom Paypal buttons.
When using Paypal, it's difficult to get the system well integrated into your website, as clients will pay, and then end up on the Paypal page with a weird link that has your email address as the name. See Screenshot:
I'm not sure if you can do an auto-redirect with a normal, free account. But here is the solution I found. Simply add a custom button at the end of checkout that says something like 'CLICK HERE TO FINISH PROCESS', (or something like that).
Step 1: Create a custom button, go to the Merchant Services Tab.
Step 2: Create a custom button.
Step 3: Give your button a name.
Step 4: Go down to '3. Customize Advanced Features'.
Step 5: Enter the link where you want your customer to go after payment. Then, enter this custom code in the box under that.
cbt=THIS TEXT WILL BE A BUTTON.
The end result will look like this at checkout
I like to use text like 'Click Here to Finish Your Order (required).' Hope that helps some people out as it took me a couple of hours of searching on the Internet to find a solution to this problem that was reasonable.