With respect Jeff eBay already pitches private sellers against sponsored links, and hide store contents from default searches and take money from both sides, and this is not off topic because:-
They get extra business via you which probably costs you money and against that they do not want you providing free image hosting and taking users away from using their own turbo lister.
Strikes me that eBay Vs sellers is very similar to eBay Vs certified service providers like yourself.
So why would they worry if you are seen in bad light, and so why should they warn sellers about thier anit-hijack listing pulls if they go to a 3rd party.
I am afraid whilst they take this apparent stance of setting everyone against each other (and taking everyones $$) all you can do is put up the warning yourself. It appears to me that you like eBay have no near competition so why would it be a problem.
It is causing increasing frustration and ill feeling and as the problem is only seen when new clients join Auctiva with active listings on eBay so you unfortunately are going to get the blame regardless.
Unless you can get eBay to listen you are going to keep getting all the flack while eBay counts its $$ and like M$ I think very few if any organisations have the clout to take them on.