A gun's value is determined by a combination of many factors, including maker, gauge, grade, bbl length, chamber length, trigger(s), wood quality, stock design, date of manufacture, overall condition, etc etc etc - but ultimately it's what someone else will actually pay for it.
There are many low grade
authentic Francottes for sale on the internet - particularly 12 gauges.
Check out some of the shops @:
http://www.doublegun.com/A big issue w/ your gun, when compared to the vast majority of others, is that yours is marked as being made by 'Francotte's Arms' and does not have 'Francotte Choke Bore' on the bbls.
FWIW, a WAG on the value of yours: $425
