Cylinder 3 Misfiring

[bman11]

Took the wifes car into the mechanic after it got a engine code for cylinder 3 misfire. Mechanic replaced spark plug and wire set, but few days later same check engine code came up. Now they're saying its an issue that would cost more than the car, not worth fixing. Are they honest or just not owning up to a mistake they made? What could be wrong with the car? Thanks guys, appreciate any input