It's only ~50 miles from me and the seller wants local pickup.
That's be a no-brainer for me, I'd ask owner if I could come inspect it before bidding. If they decline, unless they are a little old lady worried about getting robbed, I'd definitely suspect owner knows it isn't "right."
If you can get to see it in person, take maglite and look down bore, take scale and weigh it, check marks closer, look underneath etc. Take a good magnet and test everything to see if really bronze or plated iron/steel.
The Galbraith fakes are made in Asia out of the cheapest yellow metal alloy they can find, NOT the high-tensile phosphor bronze the originals used, and might easily blow up. Weight is usually less than on orig. gun. Machining on down the bore may well be poor. Since the makers don't speak English they often make mistakes like "SOU" vs. "SON." If a USCG piece, it should have the tiny "propellor" USCG proofmark, with one letter of "USCG" on each prop blade.
Biggest red flag is that no beast of that design (rear-trunnioned BRONZE line gun) is yet known to the world. Having two DIFFERENT known maker's names on the same gun is I think unprecedented.
Here's one final point to check. The rear trunnion (thick shaft connecting tube to carriage) on all rear-trunnion guns I've ever seen is ALWAYS steel, as it must be to resist the immense shear forces on firing. If the shaft on this one isn't steel, I'm sure it is a fantasy/fake item.