In 1983 I purchased a 1916 Standing Liberty Quarter from an owner in Coin World ,it was not slabbed as that was new then. I paid $2000. It came with a photo indicating it was MS60. It was a beautiful coin. I decided to send it in to be slabbed. Back then you had to have an authorized coin dealer to send it in for you,you paid him a fee. I was contacted by mail that it would not be graded because it was cleaned. I was very unhappy with that,so much so that I accepted an offer from that dealer for $1800. Selling the coin was the worst mistake I ever made. It was my most favorite coin I ever owned.
Just like when I sold my '83cc that I bought with my dad in Colorado. I sold it for lotr blu ray set since at the time I wasn't actively collecting and the way it was slabbed it didn't fit into my collection well. I'll never forget that and am still looking for a special one to replace it.
Yes, I love those too. I have an PCGS MS63 1917-D type 1 with a CAC sticker. I paid $495 for it and do not regret it one bit.
Back in the mid 1980's I purchased an MS-65 Isabella quarter from Helen Carmody, a dealer who specialized in commemorative halves. It had a dark yet colorful and appealing patina that was quite unmistakable. I sold it a few years later along with the rest of my collection. A five or six years ago as I was flipping through the pages of my Numismatist magazine I came upon a page which had a large photo of the Isabella quarter I had owned. It had recently sold at auction as a PR-65 for $10,000.00. Helen did not realize that the quarter was actually a proof and not a business strike. I, too, was unaware of that. The guy I sold it to sold it to an investor to add to his IRA. Neither of them probably realized it was a proof until it came back from the grading service before being put up for auction.
That's why you need to know your coin before you part with it. Last year a dear friend got two ms 1944 D/S cent from a dealers bargain bin for $2 each. Dealer thought he was selling unc 44 cents, I guess. Buyers should inquire, Sellers should know.