There are married skeezeballs looking for flings whether in person or on a site.
I know many people like to distinguish between online or in person, but it's basically the same. I've known people who've gotten burned whether online or not. Lying to your face or via a profile ends up with the same results, dosn't it? The guy never said anything either way, so it's a coin toss either way. You just have to date a lot and enjoy it and be ready to get back out there after the first few fails. It became tiring for me and I was no longer having fun. I know some who still enjoy it and I always give them props for sticking with it.
It basically depends on the person and their intentions and what they want. Some want a fling, some a relationship. It doesn't really matter where you meet them.
I've known way more people to get stung from meeting someone at church, the wholier than thou place. Yeah sure.
I had a guy friend to meet an online person and when he met her, she was eight months pregnant. Never once mentioned this obvious issue on her profile. I laughed so hard. I couldn't understand why she was wanting to date so badly...why not wait until after the baby was born?