Will Redd always have at least one real piece of art?
Solution 1:
In my experience with 4 Redd visits so far (and coroborated by several friends' Redd visits), Redd will always have one real item and 3 fakes. This makes it a puzzle to find which one is the real one, and means that if you've bought a real one, it's probably not worth it for your friends to check out Redd's.
Solution 2:
Actually today Redd has 2 pieces of real art! The worthy painting (which is never fake) and the motherly statute (the correct one with 2 children)