When you see the rifle, look at the frizzen. If the scratch marks start about dead center on the frizzen and then move down and the hammer has a definate S shape to it, then it is the old hammer. If the scratches start 3/4 of the way up the frizzen, normally that is a new frizzen. While they still have a S shaped hammer it is not as tight curled as the old ones. By the way, the old ones will shoot just fine.
Another trick I do is take a fuzzy pipe cleaner. Push that into the touch hole liner and close the frizzen to hold it. Then dump your powder, and patch and ball the rifle. Now slowly pull that pipe cleaner out of the vent hole. You now have powder behind the lip of the vent hole and you know it is clear. The old timers used a birds wing feather to do the same thing. Then when you prime the pan, it takes just a little spark to fall through that vent hole and you will have a BOOM!!
Good luck. I really enjoy shooting a flintlock. I can not explain why, but when you fire your first one, I dare you not to smile..