how is your deal rating algorithm calculated?

I've been window shopping Camaro's on your website, and I always select
your deal rating for good and great deals only. after looking at hundreds of
vehicles and manipulating the filter hundreds of times as well, I started to
use an excel sheet. then it got more advanced. then I started to find that
there is no positive or negative corelation to value of the vehicle and the car
gurus deal rating. the only thing my excel sheet can't account for is the seller
or dealer. but I have found vehicles thousands less or more than the fair
market value and your deal rating is not close. So I no longer use your deal
rating system as I find it negatively impacts my findings. I can give you real
examples, but overall, its still a fun pastime of window shopping for vehicles.
I hope you develope a better algorithm that is more reflective of apples to
apples comparison than the influence of location, dealers, and tax rates.