buyer's remorse

or buy·er re·morse

[ bahy-erz ri-mawrs or bahy-er ri-mawrs ]
/ ˈbaɪ ərz rɪˈmɔrs or ˈbaɪ ər rɪˈmɔrs /

noun

a sense of regret or uneasiness after having purchased a house, car, or other major item, especially when the acquisition involves an ongoing financial burden: We love our vacation property, but it took two years to get over our buyer’s remorse.
a sense of regret after having committed to an endorsement, policy, plan of action, etc.: Congressional leaders expressed buyer’s remorse after overriding the president’s veto.

Origin of buyer's remorse

First recorded in 1965–70