thrifty auto sales No warranty, Service dont know what there doing. gilbert Arizona

Ill start from the beginning, my sales person Mike and sales manager  were great made it very easy for me to get what i wanted and the process was very simple. they get a 5 star.  
Now the second day i had the truck the check engine light came on, No big deal rite, i took it and had it diagnosed at my mechanic's shop (family friend 15years) He told me the truck needed catalytic convertors. So the next day we went back to sign paperwork and i told them that the truck needed `cats. They wrote a "we owe" for the cats and a couple of other small things. Well after 7 trips to there shop , still no cats replaced and  have a check engine  light still on is why i'm writing this very bad review. There service dept doesnt know whats is going on and the communication level sucks. I have offered to take it to the dealer just so they can diagnosis it , but No they have to figure it out for them self and still won't believe the cats are bad !!  The quality of vehicles there are not dependable or can you trust what they are going to tell you STAY AWAY!!