If a relative buys a vehicle and that vehicle is never depreciated for taxes, do we assume the basis is the fair market value, or the retail value at the time of purchase? Or, do we act as if it had been depreciated?
That's tricky, actually.
First, as the section 1015 that you've referred to in your other question says - you take the lowest of the fair market value or the actual donor basis.
Why is it important? Consider these examples:
So, if the relative bought you a brand new car and you're the first title holder (i.e.: the relative paid, but the car was registered directly to you) - you can argue that the basis is the actual money paid. In essence you got a money gift that you used to purchase the car.
If however the relative bought the car, took the title, and then drove it 5 miles to your house and signed the title over to you - the IRS can argue that the car basis is the FMV, which is lower because it is now a used car that you got. You're the second owner. That may be a significant difference, just by driving off the lot, the car can lose 10-15% of its value.
If you got a car that's used, and the donor gives it to you - your basis is the fair market value (unless its higher than the donor's basis - in which case you get the donor's basis). You always get the lowest basis for losses (and depreciation is akin to a loss).
Now consider the situation when your relative is a business owner and used the car for business. He didn't take the depreciation, but he was entitled to. IRS can argue that the fact that he didn't take is irrelevant and reduce the donor's basis by the allowable depreciation. That may bring your loss basis to below the FMV.
I suggest you take it to a tax professional licensed in your state who will check all the facts and circumstances of your situation. Your relative might be slapped with a gift tax as well, if the car FMV is above certain amount (currently the exemption is $14000).