When I buy a property to flip, I put 20% down, and you wire your 80% to a title company. You will have put a lien on the house.
When I sell the house, you must be paid first before the transaction can be finished. You can choose the fund to be parked in an escrow account and then use it to fund another deal for me.
Your fund will be always in the escrow account when not in use, or in the house that you have a lien.
Of course, when I buy the property, I will first report to you the analysis of the market value. I only buy houses that are priced 30% lower than the market.