If something appears to be free …

… the old Earth saying, “if you are not paying for the product, you are the product.”

• Wiki:

“No such thing as a free lunch” (alternatively, “There ain’t no such thing as a free lunch”, “There is no such thing as a free lunch” or other variants) is a popular adage communicating the idea that it is impossible to get something for nothing.

The acronyms TANSTAAFL, TINSTAAFL, and TNSTAAFL are also used.

The phrase was in use by the 1930s, but its first appearance is unknown.

The “free lunch” in the saying refers to the formerly common practice in American bars of offering a “free lunch” in order to entice drinking customers.