I don't often list firearms for sale anymore (either on GunBroker or any forum), because shipping can be such a gigantic pain - I much prefer to sell locally to an FFL. But anytime I do list anything for sale, I would be happy to agree on terms here via PM, and then do the actual sale through GunBroker. That generally increases costs a bit (sales tax, fees, etc.), but GunBroker has some protections in place (up to $500, with a $100 deductable):
Under the Buyer’s Protection Program (the “BPP”), all claims under the BPP (“BPP Claims”) are subject to the following limitations, all of which are strictly enforced by GunBroker.com: Single Item: BPP Claims may only be filed on a single auction or a single purchase transaction. Where Buyer...
www.gunbroker.com
Personally, I much prefer private transactions here on the forum (for parts, reloading components, etc.), but some folks might like to finalize commitments on GunBroker. If nothing else, some scammer would have to get access to both a seller's Ruger forum password AND their GunBroker password, in order to impersonate them.
As always FWIW, IMHO, YMMV, etc., etc.