@Sami Gren I think the point of @Steve Hall 's original question on why you're self managing multiple apartment buildings/ asking if you don't want to scale up was basically to say that there are higher dollar per hour activities you can be doing than dealing with property management. If you factored in the numbers for property management into every deal you go for (which you must not be because you're asking what the avg rate is) then you could simply manage a manager rather than manage an entire building and all that goes into it. Once you find a PM that fits the bill and does a good job, you can spend your wasted time finding more deals and scaling.
To get back to the point and come away from the pointless sarcastic banter, just assume 10% average for PM. If you're 50/50 partners and you're doing all the work, why would you split evenly. Hypothetically you put the same capital down on the property, but going forward you do everything and he/she just collects a paycheck? If you HIRED a PM, then sure, the 5%/5% split between partners would make sense but since YOU are paying the full 10% in the form of labor (executing the job duties of a PM), that should come out of their end.
I guess that last part is my personal opinion on what's fair but you may have a different view. Partners usually bring either the hustle or the capital. You're bringing both and barely benefitting from it. If you really want to help your friend you should show them your whole process, including the PM so that they can then go and perform on their own. How's that saying go again?... "Give a man a fish, he eats for a day. Teach a man to fish, he eats for a lifetime."
Whatever you decide, spell everything out in a partnership agreement and be ready for a bumpy road because friends or not, when money is involved things can get stressful. Good Luck.