Favour well reputed advertising platforms like this one, Eros or Indy Companion for your searches. A great indicator is when the SP has a website of their own. It definitely adds to their credibility.
Before I built my website, when I was newer to the industry, on occasion I would send a picture doing a pose, hand sign or something of the sort for reassurance. I'm not inclined to do that anymore since I have my website, but if you're exchanging with a provider who doesn't have one then this might be a helpful little trick.
Use your judgement. If it seems too good to be true, it probably is. You aren't going to find a Ferrari for the price of a Civic haha ;)