I just bought a 1955 cent with a s over d mintmark d/d with a inverted s. As a error coin is it worth anything to collectors in gem bu condition?
The doubling on the 1955 could be Die Deterioration. So then that would make it the Poor mans Doubled Die.. Which really isn't a true Doubled Die so not worth much. For the mintmark question you really need to show pictures.
There is no use speculating until we see the coin. There are so many aspects of die wear, planchet and strike anomalies which can lead an inexpert scholar into "seeing" MM anomalies which aren't actually there that photographic evidence becomes imperative before any conclusions can be drawn. The odds against are rather large, to say the least. Not impossible, but large. Keep in mind, people have been studying this one for 60 years....
Okay, so post the photos. You keep asking what it's worth (I'm guessing the value will be that of an average cent of this date, mint, and condition), so why not provide what tools you have at your disposal that may allow us to do so.