Veyiten-li et-me'arat haMachpelah - Let him give me the Machpelah  cave

The reason it was called Machpelah is related to the expression kefel (double).  Apparently G-d had "doubled" the height of the cave in order to bury Adam's remains inside it.  The local residents had been unaware of this.  'Efron himself was also unaware of any special significance of the cave in spite of its name. He had had not reason to suspect who, it anybody, had previously been buried inside that cave (seeing that this had occurred before the Flood, how could anybody have been aware, unless Noach had found the land of Yisrael intact after the Flood).

When Avraham repeatedly spoke about 'Efron "giving" him the cave, he did not mean that he was unwilling to pay for it.  He meant that he would consider transfer of the title to that cave to him as a gift, regardless of any commercial transaction they would conclude concerning it.  In order not to be misunderstood, Avraham added the words (v9) "in return for full monetary compensation he shall give it to me."  Avraham neither asked for a gift, nor even for the field (which would have meant a loss to 'Efron - seeing he could no longer till it) all he asked for was the cave at the edge of 'Efron's field.