They are legit . Look on their site under " Terms and Conditions" . At the bottom of the page are the payments accepted. They are the payments normally accepted by legitimate gun related sellers . None listed are the digital payments that are all that the scam artists accept.
You can also do a google search on the address, when the info comes up click on the map and then click the ariel view and street view images and you can see the actual business. With scammers you usually see a residence that is for sale or rent , multi occupant commercial building with no tenants , or maybe a carwash or mini storage joint. Scams are really easy to spot and avoid if you try even just a little.