Filled In Mint Marks

I found some Canadian coins (quarters), to be exact; where the mint mark and some letters were filled in. I was told it was due to either a die break or debris (foreign material) in the die itself.
I took some to the last local coin show and a dealer grabbed them all (I had 12) for $20 bucks. As far as I was concerned, they just didn't look good and I'm not into collecting errors. I assume he was or knew something that I didn't. But for 3 dollars face I picked up a nice banknote instead
Try the error collectors. You never know

Normally they bring no premium at all. but post #2 you may have had a coin that he was looking for or you had an error that was worth more than you thought you never know. but if all you had was filled mint marks you done very well.
Gary

Filled in mintmarks occur because of either a chip or break in the mintmark or from die wear. On Lincoln cents they are very common from 1977-1982 and are not worth a premium. I would doubt any premium value for any of them, but since I don't bother with them I wouldn't know for sure on the other denominations. I do know they exist inside P mintmarks (which cents have never had) and are common, thus valueless.