Can an oxygen sensor be rigged to malfunction?

just took a used car in for its first oil change. the car is in good shape, and I have never had any indicator lights on. on my way home from the oil change, the engine malfunction light came on. according to the same place, it is the oxygen sensor. can this be rigged to go off so I spend more money? I don't intend on accusing them of anything, but kind of weary going back.