Is a 10% referral fee very popular in many trades?
The referral fee must be interesting enough to produce the required effort to do the referral.
If you are selling a product that cost $100, I won't be interested that much by $10 unless the effort required to bring that sale cost me less than $10.
If you give me only 2% of a sale of a product that cost $500, that will be the same for me (if the effort is similar.
So I would be very happy with 1% of a product of $5000 as it will generate 5 times more revenues!
You could always try different referral fees for different people, and see which one gets you the most referrals?
Remember too that you need to make a profit in the end. Don't give away the farm just to bring a new client on board.