I agree with Karin’s comments. My suggestion was made on the assumption that you have collaborated on NUMEROUS clients, respected each other’s work and wanted to enter into a partnership. How you choose to do it depends on you and your partner. But a client’s needs should always come first. Don’t refer someone to your buddy physical therapist, dietician, etc., if you know they really don’t need to see this person or they won’t be able to help their situation. Doing so would diminish your credibility as a trainer and make you come off only caring about receving referral bonuses and not caring about the client’s needs.
I believe that the person who needs to benefit the most is the client. Sometimes, there are referrals to other professionals without the reciprocity that you seem to be looking for.
When I know of somebody who can help my client, be it a dietitian, chiropractor, massage therapist or else, I will refer my client without expecting a referral in return. Often, a partnership will develop based on mutual professional respect, and that may include referrals.
I found the old adage “What goes around, comes around” to be true. I sometimes get referrals from people I don’t even know personally but when I dig around, I usually find connections made previously to somebody else.
There are too many ways to slice the pie on this. One of the common ways I have heard is having a nutritionist create a diet plan for people with special conditions (low fat, high protein, heart healthy, diabetic) and include that as part of a client’s training package.
The other way is to collaborate on a video, book, or other form of media.
I personally would love to have a nutritionist speak on my fitness video on simple things a client can do to control their diet.
I can’t provide any recommendation on the do’s/don’t because I have not worked with a nutrition coach in a partnership format.
Best of luck.