that's not a copyright issue
that's a
trademark issue
essentially, ebay inc has a right to a reputation, and you are not allowed to interfere with that right by using the ebay trademark in a way which makes people think that ebay inc is in some way endorsing your ebook
basically, you have to put in a disclaimer saying that "the authors and publishers of [ebookname] are not affiliated with ebay inc" i.e. you have to make sure that your conduct does not interfere with ebay's trademark rights...and to determine whether what you're doing is interference , you normally need to apply a number of tests
want more explanations or sample clauses? I suggest wikipedia...but if you're really stuck, I'll post some stuff