Two factors.
One, there are a lot of trolling attempts. He suspects a lot of them right off the bat and they fall flat on their face. We only see the relatively small proportion of them that get past.
Two, he wants a sweetheart really, really badly. So he falls for sweetheart trolls. He is usually pretty suspicious of them for quite a while, but if the troll is plausible enough, he figures the possibility of a sweetheart is worth the possibility of a troll. It's a calculated gamble.
It's a reasonably rational strategy, with the following fatal flaw. Suppose there was a girl who might be willing to have a cup of coffee with Chris and get to know him a little. (I'm not trying to comment on the likelihood of this, just go with the hypothetical). As soon as he starts acting suspicious and asking her to prove herself, she will walk away. He has made it so you have to be pretty dedicated to become his sweetheart. Who is going to be dedicated to becoming a sweetheart of someone they have never met? Only a troll.