Actually Mumbling, while the price tag may very well be outrageous, the pictures at hand show quite a few signs of of them being authentic. If they are photoshopped in any way, then they would have to be of a very high level. Most scammers don't go to the amount of work that would be involved for them.
So, what's the proof you ask?
First off, there's an official notice of copyright on a number of them. A number of animators back then put copyright notices on their works as a means to protect them. It even has the correct name of what studio made the first one and not the name of the later ones, which most scammers would make a mistake of.
Second sign, is the reflection of light the plastic protector would give off when a picture is taken. The person who took the picture was an average photographer at best. Even then, making something like that would be almost impossible in Photoshop.
The final sign? Basically a number of them show clumsy preserving and handling of them. Simply signs of fingerprints or small amounts of dust on the cels themselves.
I wouldn't say they are worth $4,000 each, but they are definitely authentic.
EDIT: On top of that, the feedback of the seller shows a great amount of honesty. At best, the person is still in their first year, but shows signs that they can be trusted to send the item at hand.
