Green Investor needing help on first deal

I have an opportunity to provide closing cost financing/down payment on a deal and not sure what criteria to add to protect myself as much as possible. 80% financing from hard money lender and rest has to come buyer. I came into the picture when his initial partner fell through. Closes in 2 weeks and he needs 10k. He wants to flip after work completed. 3 to 6 month estimated rehab.