free lunch

Fig. something of value that is free. (Often negative. See also There's no such thing as a free lunch.) There's always somebody who'll do anything to get a free lunch.

Something acquired without due effort or cost. For example, In politics there is no free lunch; every favor calls for repayment. This expression alludes to the custom of taverns offering food free of charge to induce customers to buy drinks. It was soon extended to other kinds of gift but is often used in a negative way, as in the example. [First half of 1800s]