Tim began his career as a Real Estate Appraiser with Home Savings of America in July 1986, where he received extensive training over the next nine years. During this time, he worked in multiple offices throughout Orange County and Los Angeles County, gaining broad market experience. In 1989, he was asked to transfer to the San Luis Obispo office.

In 1995, Tim left Home Savings of America to establish his own appraisal business. He later partnered with Stan McDonald, and together they operated as McDonald & Gillis Appraisal Service for 24 years. When Stan relocated to Texas, Tim continued the practice independently, transitioning to a home-based office. Tim has over 39 years of experience and appraised property in five different countries. In addition, he has been qualified as professional witness in two different countries.