The Ostrovtza Rebbe, one of the great leaders of early 20th century Polish Jewry, interpreted the dialogue between Avraham Avinu and Efron based on the Gemara here that a sale made under duress is valid, while a gift under duress is not (see Rashbam here).

Avraham announced to Efron that "Ger v'Toshav Anochi Imachem" -- "I am both a newcomer and a full resident of this land." Rashi interprets that Avraham threatened Efron that if Efron does not permit him to purchase it as a newcomer to the land, he will appropriate it lawfully since Eretz Yisrael was already given to him by Hash-m.

Efron schemed to have the Ma'aras ha'Machpelah remain in his hands by offering it as a gift to Avraham Avinu -- a gift under duress made in response to Avraham's threat to appropriate it. Pointing to the Rashbam who hints at this, the Ostrovtza Rebbe says that "va'Yishma Avraham" means that Avraham Avinu understood Efron's plan. Avraham therefore refused to accept it as a gift -- which would be invalid due to his earlier threat. Instead, he insisted on purchasing it, resulting in a valid tranaction even under duress.

Avraham Phillips