It will only have collector value if it is dated before 2002, when Germany adopted the euro. If it's anything from after 1938, it won't have much collector value. If it's dated before 1938, most of the collector value is in whatever silver coins were made. The older it is the better chance of having some value, and of course, condition is the most important piece of the puzzle.
If you don't know how to tell what you have, you won't know if a coin shop is cheating you or not.