I have very high rankings for my site

a client of mine wants to redirect, and already has, from his site which now goes to my page

What if any potential problems are there by doing this? Can I loose seo or get a penalty? Is there a right or wrong way to do this?

This is a compliment from him and his group and very well may bring me more business, but I do not want to hurt my already high rankings. Any help is appreciated. Thanks in advance.