It's often assumed that Esav exchanged his Bechora for Yaakov's bowl of lentil soup, "Lechem unzid adashim." (Beraishit: 25:30)
Well, I question that premise! The passage does lend itself to that interpretation, but IMHO that is a bit imprecise.
Look at Esav's reaction. It shows him dismissing Yaakov's proposal, not giving his consent. Esav doesn't seem to say, "Deal!" Esav seems to say, "Take the Bechorah and shove it. I'm starving! Feed me. "
Given Esav's reaction - what was Yaakov's proposal?
My interpretation is simple. Yaakov was only proposing to negotiate for the Bechorah over dinner. He delayed Esav's dinner in order to induce Esav to enter into negotiations. Esav, however, completely dismissed these negotiations. Since he thought the bechorah worthless, he gave it to Yaakov. Only then did Yaakov begin to feed Esav
Go over and parse the P'suqim carefully and see which model you prefer.
To "quid pro quo" Or NOT to "quid pro quo"
Did Esav swap a dish of lentils for his Bechorah? Or did he simply refuse to bother with any haggling while starving, and so just tossed the Bechorah aside?
To be fair to the usual assumption, Yaakov did take advantage of Esav's condition, and Esav might have had "seller's remorse" after sating his appetite. The bottom line may seem a "quid pro quo" anyway.