It's been extensively cleaned and maybe some finish applied, which may diminish value among American collectors. Here, a flintlock fowling piece in nice shape, all original, has some value but not like a "one-off". For example, a Pennsylvania or New England fowling piece of the same period, if a maker could be identified, might bring $5-$10K if it was interesting. Unsigned, unattributed, or attributed to someone not highly collectable, brings less.