The question is what does "being careful" look like. One thing you can do is if you get a message, click on the account and look at the posting history. In the case of DannyDrey it is what the kids call "sus."
Network and computer security was (part of) my day job for many years and there are generally two types of bad actors on message boards. One is the low level, petty vandalism kind of unsophisticated hackers we call script kiddies. They get a program aka script on the internet that lets them break into message boards and make posts. It is like internet graffiti, and while annoying is basically harmless.
The other is people running scams. This takes a lot more work and I would not have considered the Decware classifieds a target worth the effort. But either Decware has become a big deal, or AI has made this easy or some of both because it sure looks like DannyDrey made the effort. In the AI age it is getting harder and harder to sniff out scams via DMs or email.
One thing scammers (almost) always do is insist on a "friends and family" type of payment, like Zelle or Paypal F&F that can't be disputed. When in doubt make sure your payment is reversible, or just walk away. There isn't a lot of used Decware gear for sale, but I think you are less likely to have problem if you stick to advertised sales on legit sites, esp. by sellers with a history.