I just did it myself by filling in the form. Was pretty straight forward. The fixed the numbers that were wrong on the assessment (lot size, area of finished basement, ceiling height, etc.). I also challenged the total assessment based on the recent sale price (fortunately the valuation date was coincidentally 2 months after we closed, and 2 months before ewe took possession. After I provided evidence of that, and that it had sat on the market for several months at $50K higher during the hot Toronto market, they ended up re-evaluating it very close to what we'd actually paid.
When the redid the numbers 4-years later, I thought they'd screwed me ... but I compared it to other houses around me, that had been both the original and revised values at the time I purchased, and what they were now ... and it was all pretty good!
I certainly wouldn't pay someone to do this!
