What would a 3S do with Lambda sensor when they dont know what is it. They dont offer a Lambda sensor in locally assembled Toyotas. Idont understand why do people take their Japanese used cars to 3S dealers, They would service it and source parts locally only. Once they arnt selling thoose vehicles how the on earth would they know how to fix them.
For imported cars they are as blank as a non 3S mechanic., But yes you should definitely find a reliable mechanic.
leaving it for the 3S to make sure nothing goes rong is a wrong idea