Check the persons join date
Check their post history-are they a regular user, do they contribute or is the account just being made to look like it is, with one word answers etc.
Get and check the address
Get references - ebay, mugfs, reverb, here etc. And confirm its them-mesage on that forum or online store
Get a phone number-call, text, WhatsApp etc.
Arrange to meet in person if possible.
Take a deep breath and keep your fingers crossed.
There’s no guarantee, and especially none offered here, however I’ve traded and sold here with no issues. Sometimes it’s about putting some faith in human beings.
The user you’re talking too is a regular contributor to the site and I can’t see anything to suggest there would be any issue. But it’s not my MD!