Glad that you figured out pick-up issue directly with the plug change.
since cars belong to us, we have all the right to know before hand what they are going to do on the car.
After listening to you for the problem in the car, Connecting a diagnostic computer at arrival tells the workshop what they need to do on the car with precision and accuracy. If they don't do that, means either they lack the skills or they only want to perform regular STONE AGE maintenance and RIP US off.
I HAD a 2004 Toyota Corolla 1.6 Auto Trans other then regular service (at every 5000KM Oil change and all filters replaced engine Timing Belt changed at 100,000) and tyre change at 40,000KM it gave me 189710 KM and I sold it in March 2009. The Buyer is still happy after 212849 and her fuel average is still 13Km a litre with aircon - (thats am talking about my ride in UAE)
Auto transmissions have an oil filter in it, change it when you change the Auto transmission OIL. approx. 40K or 25K under severe weather conditions.
Power Steering fluid is never changed it is only topped up, as it is providing hydraulic pressure like brake fluid does.