If you grieved your taxes, who did you use? Did you win your grievance?

Someone on here mentioned you should use an attorney over someone like Mark Lewis, a tax grievance agency, why?

If you paid more for your house than what Nassau currently appraises it for, does it matter? I called Fred Perry when we first moved into the house and told me we dont have a case b/c of this. But now 3 years later our house value still went down and our taxes went up $3k.

ETA: I already grieved them once on my own and didnt win so I would like to use someone.