When items are posted in “auctions” I presume someone has verified that they are real. When I went off that recently and purchased something on EBAY I am told it is not real.

Is there a place I can go to get a opinion - the guy who sold it says it is real and has some old documentation that kind of verifies it?

There is no practical way for us to verify the originality of every item listed on eBay that is shown on the Oldgas.com Ebay Status page. We try to configure what links are shown to filter out many of the repro fakes, but shady sellers are clever enough to game the system to get around those filters by misrepresentation.
The policy of eBay will allow you to get a refund on items paid with Paypal that are misrepresented. Do research first. Post a question on our "Online Auctions, eBay Petroliana" section asking about the originality of a specific item up for auction.
You can also rely on paid experts, such as Scott Benjamin of Petroleum Collectibles Magazine:
https://pcmpublishing.com/services.html
And Dave and Joe at The Authentication Company:
https://www.matthewstac.com/home/

Thanks good to know