Percentage Increase Year To Year

just curious if anyone could tell me if I bought a used scott number one from a dealer in 2008 what perecentage increase there would be in the purchase price if I bought it in 2009.

It depends greatly on condition, but in general there should be little to no change in retail value from 2008 to 2009. The XF and S condition stamps, or ones with exceptionally good/unusual cancels often continue to go up even if the catalog value does not go up.

The Scott catalog value for a used US #1 in VF sound condition is $600 in both the 2008 and 2009 catalogs.

I agree that there is no rule of thumb. You could visit two dealers and find that the purchase price varies widely between them.

Depending on how hungry the dealer is, it could even vary from morning to afternoon during the course of a slow show.

I personally think you need to verify the base value before you think of applying an annual increment factor. And as to those base values I think they are exagerrated and far too inflexible. So if the base is high then even if you apply a consumer price index (CPI) you are still generating an "invalid" number. Now if the base value is valid, it would make sense to apply at least the CPI year by year.