The first real estate transaction?

Perhaps it was the one between Lot and Abraham (called "Abram" in this passage) at Genesis 13: 5 et seq. I'll confine my quotation to the bit where Abram proposes the deal, verses 5 to 9.

5 And Lot also, which went with Abram, had flocks, and herds, and tents.

6 And the land was not able to bear them, that they might dwell together: for their substance was great, so that they could not dwell together.

7 And there was a strife between the herdmen of Abram's cattle and the herdmen of Lot's cattle: and the Canaanite and the Perizzite dwelled then in the land.

8 And Abram said unto Lot, Let there be no strife, I pray thee, between me and thee, and between my herdmen and thy herdmen; for we be brethren.

9 Is not the whole land before thee? separate thyself, I pray thee, from me: if thou wilt take the left hand, then I will go to the right; or if thou depart to the right hand, then I will go to the left.

As Richard Pipes wrote in his book, PROPERTY AND FREEDOM, summarizing, they: "separated their pastures in order to put an end to disputes ... and in this manner established their respective claims to a share of the land."

As against each other, and as against each others' herdsmen/employees, their claims were thereafter secure by virtue of the demarcation. They gave each other quitclaims, in effect.