The fuel injection system, the throttle plate has a lot of carbon build up

[SirDigby]

the throttle plate is not part if the fuel injection system, it is part of the air induction system. there is not anyway for carbon to build up on the throttle plate because the 1nz-fe does not have an EGR system. the only thing that passes over the throttle plate is air, maybe a little dust, and maybe a little oil from the PCV system. spark plugs are about $25 each, i think it's .5hrs labor. should run around $150-$175 for dealer to replace. $200 to wipe off the throttle plate? are you sure she didn't get an induction service too? that runs about $250 and cleans throttle body, intake manifold, top of pistons and valves. if it's a BG service, it works very well, but is not needed on a yaris unless the car spends a lot of time idling and driving at low RPM's for over 200,000 miles or the use of poor quality fuel for extended period of time.
turn signals and wipers are a safety concern. they should have been checked first. always get a second opinion on any "service."