At anytime - did they flush out the old brake fluid when they did the brakes? Chances are - the fluid is contaminated with moisture and potentially causing problems with corrosion. Could be an issue with the ABS unit - fluid has to be regularly replaced or damage to the ABS unit may occur. A problem of the ABS system locking the brakes is a common issue when the brass valves inside go bad.
I would also be looking at mechanical issues - bent wheel or damage hub causing excessive vibration in the wheel assembly. This could severly shorten brake component life. Rotors and calipers should always be replaced in pairs - key points have to be greased for proper operation like greasing the sliding pins with high temp disc grease, greasing pad/caliper contact points on torque plate (this is what holds the caliper). The choice of brake fluid is also important - should be DOT 3 or better, but not DOT 5 (silicone based) - will cause braking issues. If this is an intermittent problem - I would have them scan the ABS computer for any preset trouble codes - ABS system could be confused and will try and lock the brakes when not needed.
2002 Corolla S, Silverstream, 1.8L 1ZZ-FE (VVT-i)
2003 Matrix XRS, Cosmic Blue, 1.8L 2ZZ-GE (VVTL-i) - RIP
2009 Matrix XRS, Blue Streak, 2.4L 2AZ-FE (VVT-i)
