As stated, value of ANY firearm depends of oversall condition. Also, what is the age of the firearm ??? That is determined by the serial number.
If I asked "what is the value of a Chevy bronco" Questions would be, when made, mileage, body condition, chrome condition, tire condition, glass condition, accidents ??? etc, etc........
You have to spell it out whatever you want to sell. You will never have a gun shop answer the question because they don't know what the gun looks like............
But, I'm sure a gun dealer would offer you $50-$75 spot cash...........................
Your colt agent was made in 1964.
Blue Book of Gun Values
100-1000+ depending on exactly what it is.
If your colt is the thunderer model (you do not say) then it was made in 1902.
value depends on overall condition.................
value depends on overall condition, model ..................
Colt revolver44-40serial6423103
300-500
what model, caliber. ????????
100-1000 USD
10-1000 USD depending on specifics.
100-1000 depending on specifics