Your not doing anything wrong at all. From what I can remember you can't they 'Yield Build' puts the advertisements from amazon on there as with the others; Google, and Kontera.
Hub pages does not have a affiliate program set up with eBay anymore, unless that has changed. The best place to ask is in 'help', the top right hand corner of the page. Scroll all way down on right side in last Blue/Grey box. There is an link to email someone for help.