Here's a situation where it appears that the victim didn't even register an account on the forum before getting scammed.
This is like one of 20 cases all of which include vareole, spanning a duration over multiple months (check trust page for some history).
No welcome message. View some of vareole's threads as if you were a guest user, but bear in mind your current knowledge greatly exceeds that of them. For example, you have to forget that the forum doesn't moderate scammers and forget that rank doesn't equate to reputation. Moreover, look at how generously the red (though somewhat pink) message paints the scammer: "while the bitcointalk.org administration does not verify such claims, you should proceed with extreme caution."
I'm not sure what
you imagine when you read that sentence, but I see something akin to eBay, with some malicious users having marked another as a scammer. Of course, since the administration doesn't verify the claims, they're not a verified scammer! At least since there is a link to something that tells me about trust in greater detail in the flag warning so that I may be educated and cautioned against scams.
Wait a minute!
How many people do you think wander into large forums with the expectation, "I need to be on my guard or else I will be scammed, because the forum allows scammers to stay here."