[Avraham] spoke with them, saying: “If you are willing that I bury my dead from before me, hear me, and approach for me Ephron the son of Tzohar, that he may give me his cave of Machpelah, which is in the end of his field. For the full price let him give it to me, in your midst, for a burial site.” Now Ephron dwelt/sat among the children of Heth, and Ephron the Hittite answered Abraham in the hearing of the children of Heth, of all that entered the gate of his city, saying: “No, my lord, hear me. The field I give to you, and the cave that is in it, I give to you; before the eyes of my people I give it to you; bury your dead.” (23:8-11)
There is one hard-to-understand phrase here: ועפרון יושב בתוך בני חת - “Now Ephron dwelt/sat among the children of Heth”. What does this mean and why is it mentioned?
One possibility is just to say that Ephron was already physically present and available to discuss the transaction. That's a very boring explanation but I can't rule it out. However, I also have a more interesting explanation. It relies on the following quote, regarding the prophet Elisha.
[The Shunamite woman] said unto her husband: "Look now, I have seen that this is a holy man of God, who passes by us continually. Let us make a little chamber in the attic; and let us set for him there a bed, table, stool, and candlestick; and whenever he comes to us, he will go there.” One day he came there, and he went to the upper chamber and lay there... [Then he asked the woman]: “Look, you have taken all this care for us; what is to be done for thee? Should you be mentioned to the king, or to the captain of the host?” And she answered: “I dwell among my people.” He said: “What then can be done for her?” Gehazi answered: “Indeed she has no son, and her husband is old.” (Melachim Bet 4:9-14)
At which point Elisha arranges for the woman to miraculously have a kid. But before that happened, Elisha offered to get the king and higher officials to help the woman out. She refused, with the explanation: “I dwell among my people.” Apparently this means that any special favors would make the people around her suspicious and jealous, and she valued her community more than whatever perks the king could give her.
Returning to the parsha. When it says that “Ephron dwelt/sat among the children of Heth”, perhaps this means the same thing as the Shunamite's “I dwell among my people”. Ephron would have loved to take the large payment which Avraham just offered him. But his community insisted on Avraham being able to bury for free, and Ephron felt he could not go against this. Thus, Ephron offered Avraham the land as a gift. When Avraham continued to insist on paying, Ephron was able to take the money. But still, to keep up the impression that he didn't care about the money, he continued talking as if he were giving a gift: “Land worth 400 silver shekels, what is it between us?”
Ephron was not necessarily a sleazy Middle Eastern bazaar salesman, professing generosity while manipulating the customer into paying an exorbitant price. It's also possible that he preferred to be honest, but social pressure from his countrymen forced him to present himself as more generous than he actually was.