Periodic car maintenance

I had received an email from the motor shop where I bought my car three months ago, which had let me know the information concerning the periodic maintenance of my vehicle. I went to the office and left my car at the garage for one and half hour. During this time, I went to grocery store to keep my food for a week, and went back to the office. The clerk told me that my car had no problem including engine, timing belt and tires. My car seemed to have no detectable change. I didn't need any charge. I didn't know what had occurred during the one and half hour.