Mentoring it's not the same as training.

I had a contract as a PM and my client assigned a mentor to me. I know, It's strange and I felt strange but at the end make sense because my mentor helped me to know the people from the different areas of the projects, make familiar with the tools, procedures, or in case if I need any assistance.

When I was in a Consultant company, as a PM in one of my projects the client also asked me to mentor a permie member of my team because he was going to replacing me after I leave. I'm not supposed to be in the same client forever, no problem with at and make sense for me.

You don't need to give him a full training how to be a PM but give him some guidelines.

I think that sometimes we need to measure if the relation that we have we the client it's more important than getting more money. At the end all of this it's common sense.