Advantages of Buying Used Photography Gear!
Cost and Value
I believe the number one reason why one might consider buying used photography gear is cost. Buying used gear is generally quite a bit less expensive than new gear. This allows someone to purchase higher end gear that may be within their budget rather than buying new gear and getting less options, resolution, or performance for their money. Also, it might allow someone to buy more gear within a specific budget. Camera gear, especially prosumer or professional gear, is generally very durable and well built, so used gear can be a better value for the money. Buying used might also free up funds for other aspects of photography, especially if one is running a photography business.

Established Performance...
Over the last decade or so, YouTube and social media has blown up with people doing gear reviews. Used hear has usually been out for a bit compared to a newer piece of gear. Therefore, there may be many more reviews online compared to something that was just released. This could allow you more insight on a specific piece of gear that you are looking for.

Used Retailer and My Experience...
I have been purchasing used photography gear from about 2010 until now. In fact, most gear that I buy now and plan to buy in the future will be from the used market. I was hesitant about buying used at first, as you may be. Worries I had were the fact that the gear may be messed up or that there is no warranty buying used gear. However, after talking to several well seasoned photographers I found out otherwise and they convinced me to take the plunge. There are several retailers that sell used gear and there are a few that specialize in used gear that I really trust. The three sources I use for used gear are Used Photo Pro, MPB, and KEH. The advantages of using these three places are the fact that they offer a relatively great warranty on their used gear opposed to buying off an individual. They make sure the gear that they are selling is as good as, or better than, the rating posted online. Generally, companies that sell used gear will provide some sort of rating system to describe the condition the gear is in. Usually this ranges from Excellent + or Like New to Ugly or Bargain. These three companies have provided excellent customer service for me over the years. In my opinion these three are just about neck and neck as far as which one is best. I would say that Used Photo Pro packages their gear best before shipping, but I've never had any issue with any of these three. I do want to point out a few bad experiences I've had from a couple of other retailers. I have purchased quite a bit of gear from Adorama and BH Photo Video over the years, and I've been happy with the quality and customer service from their new departments. However, twice I have bought from Adorama's used department and had to return the product as neither got to me in the condition that I had expected it to be in. The last time I bought from Adorama the front element of the lens was completely loose and detached from the lens. I have experienced a similar situation once though BH Photo's used department. I am sure many people buy great products from those two retailers used departments, but this just happens to have been my experience. Overall, I would not be hesitant buying used from a retailer. Generally they offer warranties and have return policies. Do your research and have fun!