I agree

However, the p[eople who advertise also pay eBay fees, and my guess it is a whole lot more than the FVF's that the item that their add appears on attracts.

If the add does direct them away from your listing (which seems like a really weird concept to me *but*) then it is unlikely that you will be paying the FVF on that item anyway.

eBay charge you to advertise your product for sale, they don't guarantee exclusivity or that the spot where you advertise won't contain other advertisements as well.

It's a bit rude, but what can ya do?