On the internet, sellers have the upper hand. They receive the money before shipping the item. Buyers have no such protection and scammers know this well. There are ways of mitigating most of the risk and we list those in the WTB section:
How to NOT get Scammed but many take the stand that new members represent a risk the buyer doesn't wish to take.
As s&wchad suggests, peruse the WTB section and you will see all the Scammer Alerts we post. I would guess that 99% of the scammers were new members, most less than a week with an occasional outlier who has the patience to wait a month or so. If I was looking for a particular gun and the OP contacted me, I would check him out and if things looked OK, proceed with the deal.
I would also add that membership time isn't a sure thing either. A lot of people use the same member name and password for multiple sites. The news often reports data breaches that include personal information, including names and passwords. Newer systems provide better security for passwords - for example the owner of this site couldn't tell you what your password is if his life depended on it, but that wasn't always true of the web and hackers buy the info from hacked sites on the dark web. From there, they simply Google the user name and try the password on any sites that pop up for that user name. We've had 3 instances of this in the last week. Two were caught almost instantly while the third nearly succeeded in scamming some members.
It used to be a pita to remember different passwords, but there are so many programs available that will generate very strong passwords of random characters and remember them for you, automatically plugging them in for you. Using one of these programs means you will never use the same password for more than one site and will provide you with the utmost security should a site be hacked.