How do you know how much you should pay a Realtor out of your wholesale profit?

[Kenos Duff]

I have a Realtor i am working with and she seems to be really fare.  She said she has worked with a lot of wholesalers before and that is a plus for me.  She also said she wanted to make sure i get to keep the MAX amount of profit possible which i thought is a good quality in a person i want on my power team because its humble and i personally would like to pay extra for people with that mind set in helping vs receiving.

I was wondering how to determine what would be a fare way to pay?

She mentioned a few possibilities like a percentage so i wanted to know what is a good rate that others would recommend.

Say i get a property on contract for $60,000 the ARV is $140,000 and sell it for $75,000 and earn $15,000 Assignment fee. Out of the $15,000 what would be a fare %?

Also another factor in this is... I have a list of Buyers to Sell properties to on a continues basis and for the first 2 deals i split the deal 50/50 after its 20/80 and i keep %80

in the scenario above from the $15,000 i would keep $7,500 since its my first and out of that i would pay fees to the Realtor.  

Any ideas what seems fare in this scenario?

Also how do you go about officiating it? Maybe a contractual agreement?

If its the contract for the property that i sign to assign to the buyer would it be part of the terms i add to the contract?

I'm looking forward to your reply's 

Thank You