The Black Diamond is a good rifle. It is accurate, easy to operate, and take care of. It's also backed by Thompson Center and was at one time, their top of the line rifle. BUT it is a devil for fowling. With the open breech design, if you have a scope, but a bikini on it. Also check that breech plug after ten shots or so on the range and make sure it is not seizing up.
They take longer to clean then some of the modern rifles, but are easy to shoot, well balanced, and will go off.They have a floating barrel actually. I have one. $150.00 might be fair, but it is used. I think the are selling on Natchez for $229.99 new. So if the rifle is in REAL GOOD SHAPE then that is in the ball park. People do pick them up cheaper then that on auction sites.. but ...
I hate to tell you that is a good price.