For the most part I agree.
Mrs. Miniver's prices are redic and I always get amused by them.
I also always just shake my head when people try and sell their framed posters in the frame on ebay. Especially w/o local pick-up to boot! I use to try and be a good samaritan about it. I would be like, (to paraphrase), "that's a nice SW poster you got there. But may I suggest taking it out of the frame and adding a few more pics? This way as I buyer I would feel much more comfortable with what I am bidding on. It would also sell much faster, which of course would benefit you." I usually never received a response back. Every now and then I got a "thanks, but no thanks". But that was some years ago, now it's just a waste of my time I think.
However, Cinemasterpieces, SW Space Cowboy poster is definitely rare. The price may be a tad high, but it is definitely hard to come by. I had a chance to buy one once but didn't pull the trigger. You really don't see them too often.