What’s the catch?

What's the catch?

What's the problem, drawback, detriment, or risk that I'm not privy to or able to see? A: "He said he'd lend me $20,000 to buy a new car, then I'd just pay him back whenever I'm able." B: "Whoa. What's the catch?" Why are you selling this for so little? What's the catch?
Farlex Dictionary of Idioms.

What’s the catch?

interrog. What is the drawback?; It sounds good. Are there any hidden problems? Sounds too good to be true. What’s the catch?
McGraw-Hill's Dictionary of American Slang and Colloquial Expressions
See also:
  • What's the catch?
  • a catch to (something)
  • a catch to it
  • catch to it
  • out of the loop
  • all able-bodied people
  • lend (one's) ear (to someone or something)
  • lend one's ear
  • throw mud at (one)
  • fling mud at (one)