Used camera lenses is not a simple product to purchase. It will be better and easier if inspection can be done before the purchase since the chance of buying a broken lenses or lenses with missing accessories will be significantly lower. Photography is an expensive but very popular hobby. There are many retailers that offer a wide array of brands of lenses.
The advantage to buy used lenses is that the cost is much more economical compared to buying a new lenses. Different specifications have different prices and brand names will also be more expensive but their quality will always to be up to standard.
There are many people who buy from ebay which I personally find it to be somewhat risky unless extensive due diligence have been taken. You really have to do plenty of research and ensure all recent reviews and feedback are positive. One useful tip is always look at top rated seller first since they have a proven track record.