I worked as an interpreter for LingoYou and I found myself struggling to receive the due payment. The agency indeed didn't pay me the amount due because the client's seemingly didn't want to pay the full amount. Not only I wasn't in any way protected by the agency (indeed I didn't receive all the money) but they also disappeared and I managed to receive the payment only +2 months after the job. My suggestion is to define exactly the price before the job, and do not give the availablity for additional activities related to that job if you don't have the guarantee you'll be paid.