Digital Delivery
Modern technology allows online e-commerce solutions that deliver completely automated ordering and delivery systems at little cost to the business owner. One popular solution is Shopping carts that connect to a digital delivery system, that sends downloads such as PDF or music files to be sent immediately to the purchaser.
So, how does it work? 
Pretty simply really. Like most e-commerce transactions, our happy little punters browses and adds stuff to their cart, next comes checkout via Paypal or similar. Now our digital delivery supplier steps to send the file. The shop owner may opt to enable unique download links (that expire after use) to each purchase for added security.
What does digital delivery cost? 
Many suppliers offer a pricing model based upon number of titles and space & bandwidth required to host and send the files.
Bitbuffet offers an entry level plan where $6 month allows for 10 products and 100MB of space.
Pulley offers 25 products and 100mb also for $6. Next is 50/250mb/$12, 150/750mb $24
E-junkie has a $5 month offer with unlimited downloads.
An option for WordPress sites is PHPurchase, with a one-time license fee of $49 and no monthly fees.
What can be sent? 
Pretty much anything that exists in digital format. One popular choice are E-books, usually in PDF format. Of course music is also a very common format sent by digital delivery. Be aware sending large files like video files may cause you to use a significant percentage of your website resource allowances. Review your hosting requirements and be aware that in this industry, unlimited does not mean unlimited!
Things to consider
- Keep it simple. If you only have a few products it may not even be necessary to have a cart. Carts are designed for multiple-item browse & purchase, and getting rid of them reduces complexity for the shopper and also your sites functionality.
- Affiliate programs. The internet is getting a little crowded with the many keen entrepreneurs trying to peddle their get-rich-quick schemes via pay-for PDFs so please think twice before joining their spammy ranks.