Q: What was Avraham thinking when he made his public plea to procure in perpetuity Hevron’s multi-tiered cave (Ma’ara Hamachpela). To clarify, the question here is not why Avraham desired the Cave in the first place. That can be answered very simply enough. Namely, he badly wanted it on account of its association with Adam and Eve having been buried there. Jewish tradition attests to that. Rather, the question concerns Avraham’s method of obtaining the Ma’ara Hamachpela. Shouldn't negotiations have been deliberated and discussed behind closed doors with the Cave's owner?
A: Plausibly, Avraham understood a basic reality: Well-heeled aristocrats like Efron the Hittite don't easily part with their property. Given that, the patriarch mourned and cried publicly over Sarah, his timeless princess in order to force Efron's hand. That is, once Avraham, well-known in Canaan as a saintly and revered man of God, committed himself to remain in Chevron until his last dying day, popular momentum was created. Unwittingly, the locals persuaded and tied, if you will, their mufti's (Efron’s) hands.
Parenthetically, how do we know that Efron was a local, Canaan nobleman and not, say a member of the middle or class? The verse alludes to it when it says that Avraham handed over the 400 talents of silver – given over to the merchant. Likely, this anonymous merchant refers to Efron's real estate escrow agent. To be sure, Efron wanted his money, but his high station precluded holding out his own hand in public to receive it. Presumably, a man of lower caste would not need to put up aristocratic airs, nor would he have compunction to pocket the cash on Main Street in plain view of neighbors.