Brake problem

Hello,
I have a 2003 toyota highlander with 86,000miles. Automatic/2 wheel drive. My problem is the my brakes squeak on one side and I have had all the brake pads replaced plus the rear rotors replced a year and a half ago from merchants tire. I have a warranty on it and I took it back to a different merchants tire by my house and they told me that my rear rotors need to be replaced. So I didn't get them replaced. So I took it back to the orginial place and they told me it was the rear caliper on the side that sqeaks. They said it was locking up. Now if it is locking up wouldn't my tire not move and it would smell. Also my car should pull to one side if I braked if the caliper was locking up right? Also could the sliding pins or bolts be replaced separately without replcing the whole caliper. I really don't feel like paying these people any more money if I don't have to especially sine I paid almost 700 dollars to replce the 2 rears rotors and all the brakes on front and rear. What should I do?