By the way the equipment (furnace, coil, condenser) will cost YOU somewhere around $1800 - $2400 depending on the house size.It will cost one of these shops far less than that, but of course, they will when asked say it's $3000 + worth of equipment.  

Electric coil, gas, oil.

It's the kind of person who hang's cabinets with a framing nailer, yup including on a plumb wall.

Looking someone to change AC filters and wash the outside unit coils.

Well, he didn't notice corroded coils which are leaking chemicals and mold that are extremely obvious even to the untrained eye when peeling the panel off. 

We raised their rent from $500 to $780 & they now pay for the bi-annual cleaning/servicing of the evap coil on the furnace because the smoke/nicotine residue is so heavy.