Determine the exact model, any modifications from it's original configuration, and the percent of the original finish remaining. Then look it up in The Blue Book of Gun Values, The Standard Catalog of Firearms, or Modern Guns. A standard 1897 lists (in the Catalog) for $400 in NRA Very Good condition. A Brush Gun or Trap Gun, $550; Tournament Gun or Riot Gun, $600; Trench Gun, $1200; and a Pigeon Gun, $2200.
I have no argument with the thumbnail quotation on value of 1897 Winchesters. Perhaps I'm wrong but there seems to be several considerations missing, such as: 1. Date of manufacture 2. Type barrel; e.g., full or cyl or both
Do such considerations affect value?
Bob - The major variations of this shotgun are differentiated by the model names given in the first answer and the Standard Catalog doesn't suggest any premiums for barrel lengths, chokes, gauges, take-down features, or even antique status (pre-1899). The post-1964 deductions wouldn't apply to any 1897's if I am correct that production ended before that. None were small gauge (20 or 28 ga or .410) which seem to bring extra $$. 16 gauge will be a plus in some markets and a minus in others. Antique status should increase the selling price because it makes a gun easier to sell across state lines, and I believe the US Post Office will ship an antique long gun. The other differences are more of a personal preference and what attracts one buyer may turn another away, so have little overall effect on the value.
I might add - the above statements do not apply to all firearms. For instance, Winchester 1885 or 1894 rifles have a gazillion different configurations that add or subtract from the basic values, especially on guns with 90% or more original finish.