Any car salesmen?

Carmax drops their prices too around $1500 to $2000 profit margin.
They only give dealer tradein on the car. Pull the NADA value of the vehicle.
This will be lower than the KBB. If the car is priced in that range they are unlikely to budge unless their lot is crammed full with more vehicles on the way.
Like the other posts look at the value and make and offer. If they turn it down then tell them to stop calling and go to the next.

You will also find that if you go to the next Carmax even though they say the inventory is shared, some managers are more willing to move cars if their numbers are coming up short that month, always buy in the last few days of the mionth when they are desperate to make their quotas. And be able to pay in cash if at all possible.

I hate buying cars as well, about as much fun as the dentist IMHO.
Lensjockie