on my side, i use a very simple technique to protect myself:

when a client require a long job to be developped - something that takes me more than 20 minutes to do - i ALWAYS make a Paypal Invoice to the client before starting the job, and require to be paid before the client receive the job... it is a secure way to be paid, as Paypal will make the reclaims if the client does not pay me... if the client refuse to pay me via paypal with an official email, sorry, no service...