I don't understand how you get scammed on ebay.
I bought and sold several backs and it always went well.
I just bought a back for $12000 and it went without a hitch.
You just need to heed some common sense rules.
For instance: a seller with 0 feedback on sales like this one, you don't buy a $25000 from them - $100 max.
You only consider high value items from seller with high and 100% feedback on sales - don't confuse feedback on buys with that of sales.
If there is bad grammar in the auction you walk away.
If on the face of it everything looks good, then you go do manual verification.
You converse with that person online, ask them all the questions you have, and then look at their answers and think.
If there is any red flag, then you walk away.
If it is someone selling a digital back, then verify he is a photographer.
Look at his website and google his name.
Call the number on his website to see the same person answers.
Make sure the same name is on all the accounts - ebay, paypal etc.
If you are very careful then there are a lot of great deals to be had on ebay, but of course there will always be scammers trying to take your money -- you should just make the effort and pay attention.
In my experience, whenever I bought something from a scammer and asked the money back from paypal, I always got it.
When sending an item to a buyer, you must wait 72 hours if it is a high value item. It can take 48 hours for paypal and credit card companies to notice a scam. If you ship too early then you have a problem. That also happened to me, so I went to the post sorting office and insisted on getting my package back before it left the country.