: Often used in the phrase "there's no such thing as a free lunch," meaning you can't get something for nothing. Can I Buy You Lunch? - GeoffMcDonald.com
Commonly used when someone wants to gain expert advice without paying a formal consulting fee.
Be careful not to confuse "buying lunch" with these similar-sounding idioms:
Offering a free meal in exchange for your time, knowledge, or insights.
It’s often seen as less formal and less intimidating than a night out, though it can still signal romantic intent. 4. Idiomatic Cousins