I bought a new in the box, New Model Blackhawk in 1983. The 3 Blackhawks, Super Blackhawk, and 5 Vaqueros I have bought since have all been bought used. No complaints about any of them.
Look on the gun, if it has screws on the side of the frame, its an "old model", the frame will just say Blackhawk, and it operates exactly like a Colt. Safe carry is 5 rnds, hammer down on empty chamber.
If it has pins, it is a new model (action change in 73) and will say "New Model Blackhawk". It does NOT operate like a Colt, uses a transfer bar, and is safe to carry with all 6 chambers loaded.
There is also the "converted" old model, which is an original model gun converted to the transfer bar system by Ruger.