Jim.....
I agree your calculation method to establish the cash equivalency of A CONCESSION is what FNMA states. (I'm not certain, however, that there is an exact method to extract the cash equivalency...but let's not go there now. To keep this simple, let's just use the term Concession to mean its Cash Equivalency.)
However, you and I diverge on how A cash equivalency CONCESSION must be annotated in the Grid.
From what I understand, ANY concession (applying to the Subject OR a Comp) must be adjusted negatively in the grid. That's what the FNMA guideline says. In the Comp grid is the only place it can be done.
The guideline does not say "well if this one has a concession, and this one does not, then you DON'T have to make an adjustment." That appears to be your position.
My position is as I have stated before in this and the other thread:
If a Subject has a sale concession, then that concession is entered in the grid as a negative adjustment applying to EACH comp. That's the first adjustment made across the board....which is why it comes first in the series of adjustments we make!
THEN, if a particular comp also has a Sales Concession that applied to ITS transaction, then that concession for that particular comp must also be negatively adjusted in that particular comp grid. (Not for all comps!)
So in this example, the Subject Sale Concession AND the Comp Sale Concession are additive in that singular grid column.
Your last sentence is where I really respectfully diverge from your opinion!
You're saying that the auto concession should not be 'accounted for' .... I'm saying it ABSOLUTELY must be accounted for, by making a Concession adjustment in each comp column. It's the only way we can extract the car value from the sales price of the Subject to arrive at the Subject's Cash Equivalency value.
Not doing so leaves the car value in the resulting adjusted sale prices of the comps, and therefore enables the OMV to be higher than it should be.
If the car value is not accounted for (deducted in the grid), it's value "adds to the sale price" of the property, which increases the cash equivalency value of the Subject (or to any other comp if a similar situation applies).
I think where some appraisers get confused is akin to 'at what point does the Concession actually apply' in terms of the sale price of the property.
Most inducements sellers make are INCLUDED in the Sales Price of the Property, i.e., buy my house for "X$$" and I'll INCLUDE the car. Since a car is not Real Property, its Concession value must be deducted from the Property Sale Price to arrive at the Cash Equivalency Value. Sellers add concessions to fool the public into believing that the value of the Property is its stated sales price. It's really not! It's the sales price, less the value of the concession.