Sooner or later (usually sooner) the person (or company) providing the "free lunch" will ask for a quid pro quo, something in return for the "free lunch."
BTW, here a definition of "quid pro quo" from Merriam-Webster: something given or received for something else; also: a deal arranging a quid pro quo
I never cease to be amazed by TV commercials that offer "free" things if only the viewer will call (usually a toll-free number). TV (actually, ALL) commercials are broadcast for only one reason: to separate callers from their money.
Besides, the word "free" is a misnomer. Nothing is free. Everything costs something, costs somebody time and/or resources. A service and/or product may be offered to the caller at no charge to the caller, but the thing offered is not free. Yet the commercals stlll use the word "free."
There is no free lunch
But that's just my opinion.