Answer: being unwilling to sell a vase for a price that is greater than the price you would be willing to pay to buy the vase if you didn't already own it.
Explanation: In simple words endowment effect refers to the phenomenon of psychology which states that a normal individual would be willing to retain an object that he owns rather than buying the same object when he or she do not own it.
Thus, unable to sell a vase even at a greater price that the owner would pay for that vase if he do not own is a clear depiction of endowment effect.