First thing that dictates value is scarcity or rarity. Yes, it is an 1873 rifle (as opposed to a carbine or deluxe rifle), and that is fairly uncommon anymore as they have been out of production for almost 90 years. But in order to be truly rare, it needs to be a variant or model that is hard to find or very desirable, not necessarily just old. Desirability generally goes something like early production > later production, and deluxe rifle > rifle > carbine, but not always. Special models can be extremely valuable.
Next is age, with anything made before 1898 being slightly more valuable than a similar firearm made after that date. First year or last year of production typically counts for a bit more.
Next thing that dictates value is condition, and that doesn't mean "I think it looks pretty good for an old gun", there are guidelines published as to % original finish, or in the case of antique firearms the NRA standard (excellent, fine, very good, good, fair, poor). People throw these terms around, but there are standards for classifying the condition of any firearm and they are published. Rust, dings, visible or poorly done repairs, missing parts or parts replaced with non-factory parts all detract from value (most of the time). Pitted or rusted bore, broken action parts, missing parts, broken wood, etc, are a death sentence.
Next thing that dictates value is factory options and the scarcity of those options. Yours has a tang sight. If it is a Winchester tang sight, the value goes up. If the rifle is engraved, the value goes up. If it has an unusual barrel length, the value goes up. If it was a special order gun, the value goes up. If you have a factory letter that tells condition when it left the factory and it is still in that condition, the value goes up.
If you just want to know about the rifle, you can research it online by finding the date of production (
www.proofhouse.com or
www.winchestercollector.com), what similar rifles have sold for recently, what was available when, etc. There is a bunch of information about old Winchesters online.
Good luck!