It's actually really hard to find compatible subs online. If you post all of your experiences or interests, the prospective sub reads until she finds one or more things that she thinks she would/could never do, and dismisses that Dom from consideration.

If you don't post enough detail either the sub never gives the posting a second thought or decides that the Dom is too inexperienced, or not Dom enough, to know what he wants.

It's largely the same as any other new relationship, fraught with pitfalls where the wheels can come off!