Let's go about it this way. Usually one can tell a "Bad"revolver pretty easy. It will have a sloppy loose cylinder a large easily visible b/c gap, odd fitting parts,unusual file or sanding marks,bent or broken sights,wrong screws in the side plate or hand grips,altered hammer, ill fitting grips,painted parts,poorly reblued areas,bent side plates,wobbly ejector rods...
By checking some of these areas you will weed out the truly bad choices. That's not to say that if the piece has a couple of these obvious defects it cannot be made into a fine looking shooting iron. By handling new or near new guns you will soon learn to discern the good from the bad regardless of the brand. I hope this helps and good luck!!