How Much Does Damage Affect Value?


I purchased a "mint" amp, cost roughly $1100. Well, packing was inadequate and the unit suffered corner damage on the faceplate during shipping. The damage is not a deal killer for me, but it is there. The unit was originally a 8/10, now I guess it would be a 6/10, though other than this blemish it is quite nice with next to no sign of wear. What would be a fair de-rate to the value?
smata67
Thanks for all the helpful comments. This is my first foray into real "hi-fi", other than a Thiel CS3.5 purchase, so I'm operating in new territory, nice to have a source of sound advice. The seller has agreed to refund 20% and I've accepted. I'm not going to be "happy" with the overall transaction given what has transpired (and neither is he), but it is something I believe I can live with. The damage is entirely cosmetic, the amp sounds incredible with the Thiels and I may very well have agreed to buy that amp with the defect at that price, ideally for a bit less, but not enough to quibble over. I intend on keeping it for quite a while, so resale value is secondary.

The seller was naive to believe that the packing was sufficient to withstand the rigors of UPS and showed poor judgement in doing so. It is a given they are going to drop the unit from a 3-4' height. The foam is flexible and only engages the unit for about an inch on either side. It was obvious to me that it was inadequate when I opened the box and it sounds from others' experience that UPS would agree. From what I have read on other sites, both the Postal Service and FedEx are superior shipping alternatives with regards to package care, though I would pack for the accidental drop no matter who was involved.

This is the souped up 8008 with 2 1100VA toroids instead of a single 2000VA as in the base unit, and twice the capacitance. To my admittedly rookie ears, the improvement is substantial over the Adcom, much more detail and the though the Adcom had plenty of bass, it just sound much more natural with this unit. I feel I made the right choice in amp, which helps somewhat temper the disappoint over the damage.
It looks to me that the amp was damaged before shipping as the original packing foam was used so possibly this is phony damage claim scam. Send it back don't get involved in a damage claim!!! I didn't once and am sorry I kept the unit!!!
Post removed 
Looking at the package - it looks like it was double boxed with the original foam correctly in place which would NOT be inadequate. I don't quite see how the damage could have happened though the box or I am missing something on your pictures.