So far I have enjoyed participaing on UserTesting, I think is a simple process and how it works is clear and friendly. You need to register and create a profile, the test that match you will show up for you to execute, for most of the test you have to do a screening to verify if you cover al requirements for it, but one you are a match you can execute. There are different types of test, short, regular with and without face recording along with test that require testers to participate in a live session. If you get into an issue with the execution you can contact user support, it takes a while to get answers but they will reach out to you with solutions/answers. Payment occurs as scheduled without any issue.