Due diligence is key.... don't rely on others, do whatever is necessary to protect yourself and never assume old sales ads will be there when you need them. The internet is constantly evolving. Websites disappear, people move images around in their photobucket accounts which breaks IMG links, data gets corrupted... etc. Simple solution is to screen capture or create a PDF image of all sales ads you have purchased from. That way YOU have the info stored on your computer and can reference it as needed whenever you need it. No need to set rules or police how long old sales ads stay up.