For Sale By Owner Question

[Nehemiah Weicks]

Hey everyone I am currently in the process of purchasing a home FSBO in which we've agreed that the purchase price of $490k but later on down the road I will pay them another 50k for a total of 540k. The reason why we are doing this is because this will be my 3rd home and 490k is the max that I was able to qualify for with out having to sell any properties. To protect both parties, what would be the best way to write up the additional 50k to be paid down the road? I've been told not to let escrow know about the additional payment. I would greatly appreciate any feed back.