I never had a problem with the combination of PayPal's selling buttons and a third-party secure delivery system (I'm using
LinklokIPN at present, a product you pay for once for pretty much unlimited use on a single website): It does a great job of delivering my content from my website; it requires only middling-level web expertise to set up--ie, if you can't enter basic data into one php file and your product selling pages,
ask your kids--and PayPal's cut is minimal.
Linklok is easy to set up and use, from my perspective, and requires no time in PayPal's sandbox. You use the same PayPal buttons as you do for your printed goods, then the php script automates the delivery process. All I sell is digital products--over thirty of them at the moment--and it never lets me down. I've even made some unintentional goof-ups in the php code, but have been able to isolate and fix the problem fairly quickly. (Backups are
Gooood!)
I would recommend it to anyone interested in selling digital goods from their site.