Unless you're a double afficionado, and know what your'e looking for in terms of surprises, if you're buying used, have it checked out.
Make sure the breech is tight, and that there's not excessive wear to the locking parts. The barrels on doubles are much thinner than on an auto or pump, or even a single-barrel, and are susceptible to being dented in the field more than a thicker barrel.
There were a LOT of "lower-end" doubles made, under many different names, that were intended to be used, and used hard. They were.
It's unlikely that a gun made after 1920 will have damascus barrels, but you should make sure that they're not.
aside from that, good hunting!
ETA: For a field gun, especially for upland birds, a well-balanced double is, IMO, the nicest gun to have.