Chanel is one of the most faked perfumes on ebay, most will tell you to stay away.
Sellers will not take extra photos upon request. Some do show photos of the bottom of the bottle. But even showing the bottom will not guarantee you will not get a fake. There is a number engraved on Chanel bottles not on the base but at the bottom front or back(sorry but cannot rememberto which. Not sure if it is on vintage bottles). Its very faint and doubt a photo would even show it up.