Learn what your looking at. They can be bought used online all day every day without ever buying a fake. If you can't see enough to tell, don't buy it. As said before, all you really need is the serial number as I've yet to see a fake with the letter(s) on either end which indicates year of manufacture.
https://www.leupold.com/leupold-core/core-knowledge/faqs#WhenWasMyScopeManufactured
