Covert Swapping

Tae Jin and Sun Ye are a couple, who eat, sleep, and have sex in the car because they don't even have money for a motel due to extreme poverty. Yoo Sung and his wife Sun Ye, who are suspicious men and women looking out the window at them, offer them a hard-to-reject proposal, but unlike Sun Ye, Tae Jin readily accepted it because he was in a hurry to change partners for just one day.
(Source: Korean = Movie.Naver || Translation = MDL)