Just pass on those companies that cannot give you a clear description of their process - they might be ones who don't know how to create a good translation at all! For the others, you should take the next step by asking if they can provide any evidence for the implementation of their processes. You want to make sure they walk the talk, right?

Don't mind the format of evidence. As only those leading players can get their processes clearly defined and tracked, you might need to be flexible with this because most translation companies don't have a formalized process in place at all. The most important thing is that you can be sure they do what they promise. For example, if they promise alternating TEP, ask "How can I know the translation is edited by a different translator?"