3 points of advice for online firearms sales:
1. If they have something in stock that no one else has, and they claim that they have sold 3 in the past day. They are based in China.
2. If their prices are 40% of what everyone else is charging, and they accept bitcoin. They are scammers.
3. If bad reviews are more than 5% of their total review. Then they are to be avoided.
There are so many big places like SWFA, Buds Guns and Euro Optic, the bad ones are easily avoided.
There are also a couple like Optics Planet and Impact Guns that don't always have in stock what they claim they do.