there are a LOT of people in this world who are afraid to admit they are wrong when necessary and make appropriate changes to rectify the situation. This phenomenon is not only confined to ebay sellers but can be found in all areas of life from the medical field to politics. Maybe they are afraid that if they admit a single error, then that will completely destroy any remaining credibility they have.
Generally, I will have little to do with such a person after I become aware of his behavior. I prefer to only do business with people who sell me exactly what I expected to get for my money.