I'm sure most of you don't remember Jose Carpio of Cinemonde, but from the mid-1980s to the mid-1990s, he was the premiere movie poster dealer. He published full-color catalogs with elite items (and very high prices) and he developed a strong clientele of rich and celebrity clients who did not mind paying his sky high prices.
But he specialized in items you couldn't find anywhere else, and he absolutely supported his prices. If you offered him a poster he had in his catalog for say, $500 for $250, he would buy it. This is not true of almost all other dealers with high prices.
He also argued that he was not the highest priced dealer, and he would list off ten other major dealers (like Joe Martinez of Cinema Collectors and Jerry Ohlinger) and he was right that all ten of those had prices at least as high as he did.
He stood behind his sales, and whenever a good customer would contact him and want to sell something they had purchased from Jose years before, Jose would try hard to find a new buyer for that item at a higher price, so he could make a commission, and the customer could make a profit on that item.
To me, a big issue is whether a high priced dealer uses deception to sell their items (like saying that an item is a good buy at say $550, when that item usually sells for $50) and whether they sell easily obtainable items for many multiples of their regular retail.
Those two things bother me. But if they offer items you can't find anywhere else for skyhigh prices, that doesn't bother me, and if they have higher than usual prices on commonly seen items that doesn't bother me either, as long as they are not massively over-priced.
None of you have mentioned the many eBay sellers with their massively overpriced items that are offered at Buy It Now, but I guess that's because you don't buy from them (and since the items never seem to sell, it looks like no one else does either!).
Bruce