Just by the scratches, how does someone fυck up that bad with the type of case back this is….
I don't think this has anything to do with removing the case back, and why I'm not convinced the watch wasn't like this from the seller.
Look at the photo closely...
None of the scratches extend out beyond the inner medallion are of the case back. If, as has been suggested, this was a slipping case back opener, there would be marks out further than they are here. So I'm not convinced in the slightest that the authenticators did this.
Now, should they have caught this? That's an argument that has some merit, but I can only imagine that if they did remove the case back sticker there would be some people that would absolutely go apeshit over them doing that. Not necessarily in the Omega world of collectors, but in the Rolex world, you can bet some would.
I don't think this is as cut a dried as some believe it is...
In the end the OP bought a grey market watch from someone on eBay, saved some money, and got Omega to foot the repair bill for someone else's mistakes. Who's mistakes exactly, we won't likely ever know...but the OP has come out well on this I'd say.