A few months back, I bought a .50, through GunBroker. The seller was a pawn shop and he did state that the bore was good but needed cleaning. He more or less said that he had no interest in cleaning it. Well, the price was right and I took a chance. The seller would only mail to an FFL, on my end and that confused my FFL as it was a M/L. .....
Anyway, when it was recieved, my FFL called me and said that I would not be happy with what I got. I took it home and the bore at the muzzle looked nasty. Let it soak for two days and proceeded to clean it while reading my jagged rod. Made several passes before inspecting it and to my surprise and pleasure, it came out very clean with good rifling.
This time, I got lucky.
Good luck and;
Be Safe !!!