A new client came to me with two manuscripts. He said he was Prof. N's former student. I knew Prof. N well; in fact, he is among the clients I actually met in person. Still, I hesitated a bit. Why? It's his email address, which is not related to his work unit. I think you can understand my concern, since I don't charge my clients until I finish editing their papers. What am I supposed to do? To take a chance, I decided. I believe that someone is serious enough to spend so much time writing papers in English has better things to do in life than taking advantage of hard working people like me.
I am glad that his English is not bad at all. However, he is not an experienced author, in my view. So, I just sent him one email to tell him how to improve his captions. (I always start with figures and captions, for two reasons. The first reason is to learn about the work, and the second reason is to make recommendations for improvement while I am editing the text.)