What prevents the final buyer from just buying the property and going over me?

[Niranyan Figueroa]

Ok so lets say that you are going to make a really handsome profit from an assignment of contract and still get your end buyer a good deal. What prevents the end buyer from just forfeiting on a contract right at the last minute, then your contract with the seller is voided and then your buyer just buys directly from the seller? Thanks in advance for your responses!