[JTysver]

Not sure what the complaint really is if you got them at 4% book. In the "too good to be true" category, I think this fits the bill.
There are opportunities to ask the seller about the cards prior to the sale. With the price on these being way better than the condition said they were, I would have asked to see more pics or more info on the cards. Especially since it was a common dealer who had experience at this. I would have looked at his previous feedback. Often, I'll find someone selling antique lamps etc. who may ask for a low price on old cards. That isn't this seller.

What people often don't realize is some of these dealers are putting up listings and selling consignment lots as per the real seller at a high volume pace. They are going to get some wrong. Hell, I do minimal selling and I get some wrong.

You got a good deal as it is. I'd offer them for sale on Net54. There are plenty of people who would be happy to buy the cards as they may help them complete their set.
Sell them for what you have into them if you want to sell them fast, or sell them for a profit and it will have been worth it.
Chances are, it was a mistake rather than the seller trying to rip someone off.