Befare engaging any tour operator or any vendor, always read their online reviews. If they dont have any reviews or just a few reviews, run away from such providers. Always choose someone who has lots of reviews for an extended period of time.
Secondly, always pay just a small advance amount for booking purposes, but never the full amount. The balance is always paid in person when you get the service. The exception is if it is via some well known providers like TripAdvisor or Make my trip