eBay quite often removes ebook listings for a violation of terms so don't panic if it happens to you.  The most common reasons for listings being removed are:

EBooks should be listed in the Everything else > Information products category. If you list them anywhere else, potentially eBay will eventually catch up with you.

But saying that with their new digital delivery service, you can list digital items in a huge array of categories  on eBay.com so this factor may not be so relevant on today's eBay.  The transcript below is a conversation I had with an eBay representative on eBay live:

08:48:02 theauctionreporter
My question is when selling digitally downloadable goods, are categories that I can list in still contained within the Everything Else Section or are we now allowed to list ebooks in other niche categories like Food & Wine?
08:49:07 Peter D.
You are allowed to list in most categories.
08:49:41 Peter D.
Upon selection of the digital item option you will be prompted if you are in a category that does not offer the option.
08:50:26 theauctionreporter
Has this changed recently then beacuse when I last read the policy it said to keep ebooks in the information products section?
08:51:22 Peter D.
I believe you are right. To the best of my knowledge digital items are listed elsewhere now.
08:52:35 theauctionreporter
So I will not be breaking any eBay policies if I list digital goods in other categories?
08:53:52 Peter D.
The system will not allow you, even if you do violate the listing policy our Trust and Safety Department will remove your listing at no charge with a friendly reminder on how to correct the error. 

If you write an ebook, you must state in your auction that you are the copyright owner something like “Note to eBay: I am this ebook's author and own the copyright to this product”.

 If you are reselling an ebook you should state in your auction something like “Note to eBay: I am a licensed distributor of this ebook and have resale rights to this item.

Obviously if you do not have resell rights don't sell it, you will eventually get into trouble from eBay or the ebook's author.

I got one of my ebooks withdrawn for having a misleading keyword in my title.  I was selling a police auction ebook and out x-box in the title and I wasn't selling an x-box obviously so it was taken down.  I only had a one day listing for that item so they are on the ball.  Don't use keywords that do not accurately describe your item or violate any trademarks.

Things like “make a million in a hour” (I wish) is a misleading title and is not accurate  so make sure your titles are accurate.  

Selling only 1 cent ebooks can be another reason for your listing to be removed because eBay see that as solicitating feedback.  Buying only 1 cent ebooks can also end in suspension so be careful.

If you do find one of your listings is taken off eBay, find out from eBay exactly why it has been removed.  You can do this via email or by asking an eBay live representative but be patient as instant answers from eBay is not common!

When you have found the reason relist the item making the required amendment, check with a eBay representative it is not breaking any rules and bingo you are not going against any eBay policies and you are building a good standing with eBay because you are making sure you are not breaking any rules.