I've seen real estate listing photos that have been altered by a method commonly referred to as 'PhotoShopping' to remove distracting or unsightly items like power or phone lines coming in from the street, large power or water towers in the background, etc. One has to consider the ethics of this and whether it might be grounds for a civil suit in some cases. Many real estate agencies, sensitive to this issue, state specifically that they don't alter photos the present by any means, including digital.
When it comes to selling online, whether it's real estate or costume jewelry, clothing or kitchen utensils, there may be a desire to 'PhotoShop' images to get a better look. Perhaps brightening, lightening, or sharpening an image that is slightly off due to focus or lighting is not out of line but one must consider how much is too much. Since, unlike real estate, most items sold online is purchased sight-unseen it suggests that images displayed should fairly reflect the actual item. Perhaps this is an issue that needs a little thinking.