I know it's a scam, but what's the catch?

[TsPoet]

Now, I don't know that much about bikes, but I know that anything with 105 components tends to retail around $1500 and up. If he really wanted a bike in his size, he could easily sell his expensive bike and buy a much better bike than mine in his size.
so it's got to be a scam, right? No one is that ignorant, right?

If all you know is 105 components, it might not be as big a difference as you think - frame, build, brand, size, age... He could also just be desperate like he said.
But, I would definitely bring a friend with you to meet him! You could also request that you meet at your LBS so your LBS could look his bike over and give you some advice.