Both shotguns have not been made for decades, and parts are scarce. Being Browning designs, they rarely need any parts, but since the Model 12 was THE trap gun for a long time, plenty of them are well worn. Sometimes the bolt is worn to the point where headspace becomes dangerous, and a good smith will build the bolt head back up with weld.If you buy either, a trip to a good smith is in order to check it out, as with any used firearm.
I've shot a 12 a little at clays and like it, and a well worn 97 was part of our crew equipment during the late unpleasantness in SEA. Both were good shotguns. IMO, the 12 shucks a little fasternsmoother, but it's minor.