That seller is Mike Moree and his company name is Audio Specialities. He is quite a nice fellow in my experience. He can find parts that you need often and at reasonable prices. I don't think that based on my experience with him that he is trying to rip anyone off. And I don't see a problem with him buying parts from Tascam and offering them on eBay for more than he paid. He is a small business owner and wants to make a few bucks.
Let the buyer beware. And educate the buyer rather than go after the seller in this case. The seller will drop his prices if there are no buyers.
Personally I would like to run across a primo TSR8 for $50 every day. You would see them on eBay for $600 and I would not be working for a University.
Regards, Ethan