My question is how to securely pay for a gun from a private seller in another state to ensure you don’t get scammed?
I already know about how to get it shipped into the state.
Just want some security to avoid a scam.

Any advice is greatly appreciated!
Mahalo!

I used an escrow service to buy an expensive bicycle on ebay about 15 years ago.  I put money into the account, they shipped the item, I inspected it, then released the funds.  There was an extra fee I had to pay.

Since you will have to go through an FFL here, you could have the seller get in touch with your FFL.  The FFL can play middleman. 

1)  seller ships gun to your FFL
2)  FFL receives gun & notifies you
3)  you inspect gun
4)  if satisfied, you send payment to seller
5)  seller receives/verifies payment
6)  seller notifies FFL to release gun

That assumes the FFL is willing to be the "broker." As long as the FFL doesn't give you the gun without the seller's okay, everything else is no different than you'd do normally.

It's a square dance, but it's not that complicated.

Ideally, you want to use a payment method that you can cancel if there's sign of a scam. When I bought online, I always used a credit card.  That way, if the deal went south, I had the credit card's buyer protection on my side.  Just because the seller isn't a dealer doesn't mean there's no way for them to accept a credit card payment.  I paid a 3% CC fee, but it's worth the peace of mind and protection.