Yes, there are many reproductions out there, especially in the world of Red Wing, as the factory sold it's many molds to private individuals and schools when they shut down in 1967.  Especially when purchasing over the web, it's very difficult to detect a reproduction as a mere picture (unless it's in great detail) will not tip you off .

Here are some tips to find those reproductions:

1. Check the Weight - Quite often a reproduction is not made of the same clay used by the original manufacturer and there will be a significant difference (plus or minus) from an original.
2. Check the Size - Based on the diffent clay used in reproduction, the shrinkage of the clay after it has been removed from the mold will (typically) cause the item to be smaller than the original.
3. Check the Markings - Not everyone is trying to hide the fact that their piece is a reproduction; quite frequently you'll see initials, a name, or even a date scratched into the clay where the original manufacturers mark should be.  Especially with Red Wing, you may see a shadow of the original impressed mark but some other non-standard mark will be in place.
4. Check the Glaze - If you're really familiar with a particular line of pottery you should be able to look at the glaze (in person) and tell immediately if it's standard or not.  The shade/color of the under-glaze may be the clue; sometimes it's the exterior glaze that will tip you off as it may be too shiny or matte.