I'm uncertain of the industry standards at this time.  Would the referral fee apply to the first service or all of the services booked by that particular referred client?

Should the referral fee be a percentage of the first service booked, for example 10%?  

Or would the referral fee be a percentage of all of the services booked by that referred client?

Or would the referral fee be a flat rate for the first booked service appointment?

If anyone could lend additional guidance regarding this question it would be appreciated.