With respect, I think that you are really missing the point.
The garage is not making 2k profit,
They may get a 2k mark up if someone comes along and is stupid enough to pay the full asking price
However, at the end of the day, the garage will be lucky if they come out with £500.00 of a margin which will be subject to vat at 20% and a further 40% income tax at year end.