I would love for somebody to explain to me why people are obsessed with COA's. In what situation does one really help? If you are buying a forgery, one assumes the seller would just forge a COA. If an authentication service says it's a forgery then a COA doesn't help. Not to mention that the gallery who issues the COA likely won't be in business in ten years anyway and then you'll have a guarantee from a place that no longer exists.