Granted. That said, trusted and respected dealers don't fight it, they rarely even question it, they just honor the return.
When I was a dealer I always took returns if it was within a couple weeks of the show. I thought that it was better to keep the good will of the customer, and I was always able to sell the item again any way. The item did have to be in the original holder and unchanged from the time I sold it for me to accept the return. I think that if there is any question about authenticity, the dealer has to back the piece, no matter what. Years ago I bought a raw 1798 dime in Fine that turned out to be bad. I returned it to the dealer from whom I had purchased it. He could not see that it was bad, but I saw it once I REALLY looked at it with at stong glass. It was a darn good counterfeit. The coin had been sold in a Dave Bowers auction. Dave made good on the piece on the piece despite the fact that the sale had been months ago. That's what a professional dealer has to do. The one place where I have make an exception about returns would be bullion. You can't buy a piece of gold, silver or anything else one week and expect to return the next week because the price went down on the metal. The customer should not be able to play the market with my money.
In general, I don’t return coins. If I find out later that I don’t like it, I misattributed the coin from the pictures, can’t make money on it, or I overpaid due to improper research, it is my responsibility to deal with the coin, not the seller’s. At that point I just sell it and hope break even/make a profit. There are some very specific circumstances in which I will return a coin: 1. Authenticity issues. I’ve returned many a fake coin, even those that were just questiinable, and gotten refunds. If the fake is from a lot and that coin was one of the main reasons I got the lot, then I try to seek a partial refund. 2. Grossy misdescribed. This is reserved for when the seller fails to mention, for example, the coin had been professionally holed and plugged. Another example is when a coin was described as a proof and turned out to be a cleaned business strike. This is rare for me, and I have never had an issue. 3. Scam. One time I bought one coin, and the seller deliberately tried sending me a clearly different coin (the pictured coin was EF/AU, the coin I got was G). I was successful returning that one. 4. Honest mistakes. Maybe the seller mixed up packages (I have done so before). I have not had many of these (none come to mind at the moment). 5. Not meeting the guarantee. This one is hypothetical. For example, if the seller guaranteed, in writing, that the coin would straight-grade and doesn’t, I will try to return it.