Kosinar: Before you buy any gun, be sure that the dimensions fit you. Most Fox guns have a lot of drop at the comb and heel. I, for one, can't shoot a gun with 3" of drop at heel.
If you are set on getting a Sterlingworth, realize that you should have someone knowledgeable check the gun for you. Most inexpensive, and maybe most 70-80 year old guns have accumulated wear. Even the Sterly's priced in the high teens. These days, it seems common to see 16 bore Stery's for $1500-1800. That still doesn't mean they are worth the money. 20 bores are even more expensive.
One other thing. We Americans seem preoccupied with old guns in original condition. Although original might indicate the gun hasn't been poorly modified, it doesn't mean it is a "collector." Low condition guns are common, and are only collectors to the uninitated.
If a Sterly has been modified, and refurbished, do look it over. I for one use my guns all the time, and have refurbished actions and other needs as necessary. I usually contract a knowledgable "smith, although there are many things I do well myself. I know where to get help when I need it.
If you insist on buying an old American gun for a piece of "Americana" good liuck shooting it. Remeber...have someone give it a hard look. Mike