There are a range of things we can do to improve the appearance of a stamp.
In another thread I showed images of a stamp that looks to have had rust removed (here:
https://goscf.com/t/17003)or should I more correctly say the appearance of the rust has been altered. I think this is manipulation that should be advised to the purchaser. I don't think these treatments are in any way permanent and the stain returns in pretty quick time.
If a used or mint-no-gum stamp has a hinge remainder or gum that is toned or discoloured, as you being misleading by removing these to create a stamp that is more pleasing to the eye (both from the back and front. It is surprising how much surface grime accumulates on a stamp over 100 years)?
I saw a Melbourne dealer many years use stamp tongs rubbed briskly on the back of a heavily hinged mint stamp to create heat that allowed the hinge remainder to fall off. He then 'polished' the gum with french chalk spread on the desk to transform a heavily hinged stamp with hinge remainder to a lightly hinged stamp with much fresher looking gum. Is this acceptable?
Obviously plenty of discussion is being held in the stamp world about added perfins, reperforating and regumming, all of which are clearly fraudulent IMHO. (oh, forget the 'H', I'm not humble but I am probably more humble than Rupert Murdoch!).
My view is that you have a stamp and you have foreign matter. Removal of foreign matter is acceptable (I give all my used stamps with hinge remainders a bath in hot water so that only the stamp remains) but any manipulation of the physical stamp itself to present it as something other than original item delivered from the printer to the post office is unacceptable.
The treatment of rust falls in the middle somewhere. I wasn't on the stamp originally but I don't think it is foreign matter either as it becomes part of the stamp.
What are your thoughts?