How much to pay for a referral???

[Matt Nico]

Hey BP!!!   Real estate investor and new real estate agent here!!!                    

Referral based Question:

I have a neighbor who got me in contact with a person who was looking to sell 4 properties off market one at a time. I contacted him, and everything worked out great on the first one and I bought it 4 weeks ago and am right in the middle of the rehab. 

How much should I pay my neighbor for giving me this contact information? Do you have a set price, a % of the purchase price, or does it vary based on the kind of deal you got?

Also, when does this referral get paid? After the house is purchased or after the rehab is completed and the home is rented?

Thanks in advance for your input,

-Matt