I'm a firm believer that the poop's gonna hit the fan in my lifetime. Between my AK's, mini 14, dad's Garand and M1-A, and zillions of rounds of ammo, I'll be the Negan of the neighborhood!
gunbroker is also good but just be careful and make sure you read the Item Description and shipping charges. I think this is why I like Buds so much. Free shipping to your FFL on all guns and their prices are about as cheap as you can get anywhere
I have never bought a firearm online, but I have bought quite a few at gun shows. You just need to know what you are looking for and what you are willing to pay for it.
Classic Firearms is a Christian seller but they tend to deal in surplus military. However, the have been upping their game, and their prices lately and since Obama they can't get the same guns they used to. Still, the have been very honest and might be worth trying.