I use a site called People Per Hour rather a lot.
I’ve been on there for some years, and have found a pretty good way to isolate people who are going to be poor to work with.
100% of clients who write to me three times in a row without a response have been crap. Now, I suaully get back to all message son there within a couple of hours, so that gives you an idea of how quickly they’re trying to chase me up, even before I’ve had a chance to say hello.