Idiom: What's the catch?
Meaning: It sounds good, but are there any hidden problems?
Two friends, Arda and Joao are talking about buying a car
Arda: My friend is selling his car for $1000
Joao: Sounds too good to be true. What's the catch?
Arda: The air condition in the car doesn't work
Joao: Now I understand why he is selling it for such a low price.