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Phrase(s): There’s no such thing as a free lunch. [and] There ain’t no such thing as a free lunch.
Prov. Cliché Everything costs something. (Can imply that you should be suspicious of anything that appears to be free.) • Fred: This advertisement says I can get an expensive camera for free! Jane: Don’t be so gullible. There’s no such thing as a free lunch. • Mary gave me her sewing machine, but I had to give it $100 worth of repairs before I could even use it. There’s no such thing as a free lunch.
McGrawhill's American Idioms And Phrasal Verbs