How Much Should Damage History Affect Value?

[BoxMann]

I'm looking at a Boxster that shows rear end collision on the Carfax. Happened over 10 years ago, not with my Seller, but with the prior owner. Seller says he was told it was a very minor low speed impact and only required repair (not replacement) of the rear bumper cover and nothing else. Work was professionally done, and the current pictures don't show any signs of damage. No photos of the original damage, no body shop bill. I asked.

I have no reason to doubt my Seller, however, the fact of the matter is, is that he doesn't really know what happened, nor do I. So let's assume that it is in fact the minor low speed damage that it was stated to be, doesn't affect appearance and driveability, and that nothing is uncovered on a PPI regarding this. Fact still remains that it is a stain on the vehicle's history. Obviously, if you hypothetically took two identical cars, one with this history, one without, the one with the damage history is going to sell for less. (Many buyers won't even consider a car with damage history, even if minor and professionally, competently repaired.)

So how much less? On an '03 I would figure there should be roughly a $2,000 difference. Sound about right, assuming the above facts?