There is an element of trust involved in online sales.
Make sure you at least get a phone number and speak directly to them.
Bank transfers are normal.
Paying in full before any transfer is also normal.
I have honestly not heard of any dodgy business going on once money is transferred.
A bank account will also give you a starting point should you need to trace, as well as a phone number.
The feds would take an extremely dim view of firearm sales shenanigans.
On their part
Any photos requested should be provided promptly
Full disclosure of condition
Trust but verify.
On my part , I expect prompt responses to questions. Zero tolerance for BS.
Any stupid stuff like " can’t take a photo, it’s at my mates house" etc.
Any reluctance to full disclosure
Any lies or mucking me around with dates, info etc.