If you are planning to sell on eBay , it's not really a good idea because eventually you will get banned for it within few days.
I tried it myself , i sold many keys and then after few days they banned me for doing that.
Good luck mate !
If anyone is still interested in purchasing keys I've got 100% authentic retail keys that can be purchased in bulk and re-sold legitimately on your own store. Some of my inventory is the following:
Office 2010 Professional
Office 2010 Home and Student
Office 2010 Home and Business
Office 2013 Professional
Office 2013 Home and Student
Office 2013 Home and Business
Office 2011 for Mac Home and business