If I buy an item off eBay, am I allowed to repost the item on eBay.

And if I can, then can I post it for more money?

Dave, once you own the item, you can do whatever you want, including reselling it on ebay for more than you paid.

Don't re-use any photos or word-for-word descriptions provided by the person who sold it to you. While the item is yours, those are not.