If it has a beavertail forend, it is probably a replacement, the only way to know for sure is to take the forend iron off the wood and see if there is a stamped serial number in the wood, usually on the end where the forend metal mates to the receiver.
L.C. Smiths were famous for loosing the forends because in order to take them apart you have to re-cock them, then take the forend off and barrels from the receiver. You will put a lot of pressure on the "J" spring and bend it.
As far as cracks behind the sideplates, that is true, because most people who shoot them now, shoot higher psi shells than you should. You should really shoot only shells with about 8,000 psi.
Also, if a 1948, it will have 2 3/4" chambers. Earlier ones before 1936 had 2 1/2" chambers.
Ask to take it apart, or have them take it apart and see if the serial numbers match on the parts you can see, forend iron, barrels, receiver. Write the serial number down and myself or someone will verify what year it was made.
