You can post Ebay products in Ebay capsules on your hub. It must be a product that is related to your hub.
Promotion of personal websites etc. is frowned upon. for 2 reasons. 1) You would profit from leading people to your website. 2) You would be leading viewers away from HP.
You would probably be reported for self-promotion/ overly promotional content.
There is extensive information in the learning center. HP is not a free advertising resource.