well ya got to get ur fingers dirty
To determine exact value of a 1904 Marlin 12 gauge pump shotgun, you would actually have to take a number of factors into consideration. The main thing to consider would be the condition of the shotgun.
Best left to a gunsmith.
50-300 USD, 12 gauge pump
See the link below for instructions.
marlin 12 gauge bolt action goose guns sell for about $200 in great condition
50-200 USD
50-150 USD
100-300 USD
50-160
100-1000 USD
$1,000,000.00
50-250 usd