What is supposed to prevent a commercial crew from flying to the wrong airport?
According to the Wikipedia article on IFR: 


  VFR is the most common mode of operation for small craft. However, it is only safe to fly VFR when these outside references can be clearly seen from a sufficient distance; when flying through or above clouds, or in fog, rain, dust or similar low-level weather conditions, these references can be obscured.


So basically, a pilot would land at a wrong airport due to one of the following conditions:


He/She did not have previous experience of landing at the said airport
He/She paid more attention to VFR that IFR (which is usually suggested), and the proximity of the airports confused him/her



  Any aircraft operating under VFR must have the required equipment on board, as described in FAR Part 91.205[5] (which includes some instruments necessary for IFR flight). VFR pilots may use cockpit instruments as secondary aids to navigation and orientation, but are not required to; the view outside of the aircraft is the primary source for keeping the aircraft straight and level (orientation), flying to the intended destination (navigation), and not hitting anything (separation).


This means that a pilor following VFR can get confused, and that would be a completely manual error. To prevent this from happening, he/she should raise a flag with the Control Tower before landing if his IFR shows a different destination, when compared to the place he is intending to land at following VFR.