Amen Joey. I can't stress it enough on brakes. I see far too many people that come in and want to replace just one to save $.

There is also alot of moving parts inside the caliper as well, slide pins, piston, etc. Both can cause the caliper to lock up. Not to mention a blockage of the hose itself. Sometimes they can be rebuilt, sometimes you are better off going with a loaded caliper for a replacement.
Good luck