Q: I have a 2012 Infiniti QX56 and went through exactly what this person did with the truck going to the dealer in perfect order and

A/C systems that are leaking will function up to a "threshold", that is a minimum level of refrigerant charge, but once the charge drops below that threshold the system’s low pressure cut off switch will shut down the compressor. The low pressure switch is there to protect the compressor because the compressor oil circulates with the refrigerant and if there is too little refrigerant, there is too little circulating oil. In your circumstance, the ONLY way to determine conclusively if the shop broke something is to know the state of charge (amount of refrigerant) before you gave them the car, the leak rate, and whether or not the subsequent failure was due to a sudden enlargement of the leak (e.g., a pin hole blowout in a condenser which will empty the system in seconds) and when the enlargement occurred (e.g., shop accident or on the road?). The problem is the missing data make any determination impossible. One oddity in your case though, as you put the pieces of this puzzle together, is the fact that the recall involved a possible defect in the fuel pressure sensor. Work on that sensor does not implicate the air conditioning system at all and so in composing my response to you, I am puzzled as to why they ended up diagnosing a system on your vehicle, the A/C system, when that system had absolutely nothing to do with the specific recall and perhaps you did not even authorize that a/c diagnostic?

Regarding your question of to how to avoid rip-offs. The only known, absolutely guaranteed, tactic to avoid ripoffs is to perform your own repairs. A next best option, which is workable, is to hire a PERSON, through services such as YourMechanic. Note, PERSON, in all caps, as opposed to a shop. When you work hand-in-hand with a person, you can ask lots of questions, directly observe the work, make special requests as to parts, use your own parts, and on and on with no limitation. YourMechanic is a service that can potentially help the public avoid rip-offs, overcharges, and lousy work performed at conventional shops. If you have further questions or concerns, do not hesitate to re-contact YourMechanic as we are always here to help you.