No you seem to be. MANY including myself have purchased Apple Care from EBAY in the past and later found out it GOT DENIED because they wanted a RECEIPT or the BOX Serial # which we had neither because they won't accept EBAY receipts and the sellers normally don't send out the BOX.
The point is, people can not expect to buy Applecare on ebay and have coverage as APPLE is cracking down on this now.
We sell nearly 1,000 Applecare boxes a month in 11 countries, and there has NEVER been a case where a client has had its AppleCare coverage denied, so your generalities here are misplaced. We buy AppleCare boxes directly from Apple by the truckload (and we must buy them as Apple's highest retailer discount depends on us buying Applecare for 40% of the Macs we buy...) and thus any general statement that buying AppleCare on eBay is dangerous, is plain silly. Like anywhere else, it is the quality of the seller that matter and not eBay as a forum...
OP's problem is that he can't provide proper proof of purchase.
Wrong, his problem is that he is attempting to register AppleCare after the deadline for its eligibility has expired. We have a recent letter on file from Apple which confirms that Apple will register AppleCare regardless of whether it was purchased through Apple or not (failure to do so would be a major anti-trust law breach), and thus it makes not a hoot of difference whether the seller is an Apple dealer or not. We have an excerpt of this letter on all of our listings, so you can easily read it for yourself.