Basically, the GB approach now is, Sorry, but good luck if you get screwed by a seller when buying through our site. We can't do anything to help you, but you can leave a bad review for the seller. They do have a Buyer Protection Program that you can attempt to use, but it sounds like a drawn-out, months-long process that would be more trouble than it'd be worth in most cases. If it even works.Gunbroker is a mess now, all good till there is an issue like the OP has and then you're just doinked (putting that mildly).
Had a shady seller send me used parts as new, clearly he was wrong but GB doesn't care and you can't reach a person in this lifetime. When they got sold, it went to a "marketplace" seller who does not care about doing right nor the firearms community. They could just as easily be selling wool or beanie babies so long as they get their %.
I have about 50 transactions on GB, mostly back in 2020 and prior when the charges and fees were reasonable. Recently I made the mistake of "winning" an auction for a gun that looked like a decent deal, but I failed to count up all the add-ons. The OTD price with shipping, taxes and fees, credit card upcharge, and all came to an additional 20% on the purchase price. Hopefully these new GB fees and taxes and all will help local gun shops win more business to help them actually stay in business. I just wish the LGS had guns that interest me.