Alot of the ebooks that you will see listed with resell rights will be in fact old or out of date.
However alot of the ebooks, even though they are old, can still be in demand. you just need to look through the listings and see which ones are most popular and still selling and use those books..You can easily do this by using the completed listings feature on ebay and by visiting some of the forums on the net..
As JT Ktd said, you can easily automate the whole process very easily and once you do that it will practiclly run itself...Most people who are buying ebooks want delivery as soon as they pay, so setting up an auto-delivery and payment system is a must...
In addition, there are several good softwares that you can buy for creating your own ebooks to sell in addition to the ones you purchase with resell rights to sell. Instant Article Wizard is very fast and easy to use and you can create an ebook in just a few minutes. Another thing you will probably want to look at is a software for putting the ebooks that you create into some sort of 'reader' format so that you can easily deliver them and the buyers can easily open and read them. The most popular is probably adobe reader and you can get software such as 'pdf995'
which will convert your books into an adobe reader format..