If your friends found out you were being taken in by an internet scammer, and they had a way to prove it, would they tell you? You'd probably say "Of course!"
Unfortunately that's not how people work. For instance I know of a case where a woman is totally obsessed with this guy she met on an internet dating site. He's saying he's going to prove how much he trusts her by sending her thousands of dollars, which she should then send back, just to prove than he can trust her too. This is a Romance Scam combined with a Fake Cheque Scam. Obvious to anyone, except the victim of course, who has never heard of either. Her friend is suspicious and told her not to have any financial dealings with this guy, and she promised she wouldn't, but of course if she doesn't the romance is over so she'll probably end up doing it anyway.
The woman's friend doesn't want to take the next step which is to prove that he IS a scammer. She can do this two ways- she can get the guy's photo forwarded to her and check it against known scammers on this site, or get his e-mail address and check it against known scammers on this site. But she doesn't want to do this because she herself doesn't want it to be true. She doesn't even want to warn her friend because her friend will hate her for it. After all, people who are in love don't want to hear anything bad about their lover right? And even if the woman believes her, well it's going break her heart.
So the easy way out is to just leave the poor woman in her deluded state, wait until she's been taken and listen sympathetically to her while she suffers the heartbreak that was always going to happen, and the humiliation of having been cheated out of money that she couldn't afford to lose. The woman will think her friend is a wonderful person for being so supportive. So that's the option her friend is probably going to take. That's human nature.
Worst thing is, the woman met this guy through a Christian dating site. When her friend warned her not to give the guy money she replied that she was sure God would look out for her. God did. He sent her someone who could prove to her she was being scammed. If her friend doesn't do it however then the woman will believe God let her down. Which He didn't. I'm trying to convince her friend to tell her (I don't even know her name), but if I push too hard, I will lose a friend too. And so it goes. So the strongest allies to a scammer turn out to be the victim's best friends, who won't tell even if they know about it.
Lovely isn't it?
http://www.romancescam.com/album/ has some of the most common photos used, http://www.romancescam.com/ has more ways you can tell if you are dealing with a scammer.
A high percentage of the listings on dating sites are put there by scammers, so look out!