OK, I had to answer my own question!
Using the SEO Book again (I think I might have to add these guys to my blogroll) the closest keywords/phrases that would fit a company selling ebay design are:
make money on ebay – 22,614 apm
ebay business – 27,090 apm
*apm = average search volume per month
and in order to run a successful Google Adwords campaign a lot of ebay related negative keywords ( keywords that might contain ebay but are so not what you do and will waste your precious moolah man!) Most searched to do with ebay are from ebay users and not the ebay sellers you would want to push ebay design too? So how would an advertising campaign start? To maximise the return on investment you would need targeted traffic, and not 7 million ebay users who don’t care two hoots about ebay design!
The keywords ebay design, ebay store design, ebay template design and ebay listing design need to be within your campaign as your competitors also use these keywords and you do have to make sure you are not left behind, but how do you make sure you are hitting the right people?
Answers on a postcard please!