Used can be good or bad deals. Being new to the sport it can be hard to tell. 90% of my local Craig's list ads are junk. "I paid $2000 for all top of the line gear and letting it go for $800" is a bunch of out of date junk that was bought new in '86 and has been sitting in a box in the garage since the one trip they did to Hawaii in '87. I wouldn't trust it for anything more then something to play with in a pool. And that would be after it was went through. On a good day might actually be worth $100 just so you don't keep dunking good gear in chlorine. Or you see ads for fairly new gear with MSRP prices quoted and asking prices almost for what you could actually buy it new for. Add in are you willing to buy something that someone else has decided wasn't good enough to keep?
Brick and mortar stores are good. Most that are standing today know that the internet exists and you can buy there as well. You have to ask for the deal on pricing. It's a bit like buying a car, there is the price on the sticker and then the price you can get out the door. Don't beat up the local shop too much, remember you can't buy air on the internet. You will need to have a good reputation with your local shop. That can do wonders for little things later when it matters. I've been able to test dive gear in person after getting to know the staff. Ever wonder if that other fin style works for you? The owner loans you his pair, you try them, now you know. You are not going to get that with an e-store. That is why you NEED to get a reputation with your local dive shop.
Do I buy used? 20+ years later I still buy some used. Just bought a pair of tanks. I knew what they were, what I would be using them for, what would need to be invested in them to use them. Without knowing what you are looking at, looking for gear gets hard. There are plenty of bad choices available. I see plenty of used tanks on the market that by the time you bought it and brought it up to standards (hydro, vis, fill) you are at what a new tank would cost. Shops have used gear as well. Everything from last year's rental gear, trade ins, I even know some that will spot the bargains and snag them for a quick resell at a fair price. One thing the shops don't want is a bad reputation, they will generally avoid selling complete junk (unless that is what they are selling for the purpose of scrap metal, learning the basics of a regulator operation, art projects, etc.). But they will be specifically selling it as "junk parts", by the pound.
Even something a mundane as a wetsuit takes a bit of research. Lots of 90's 7mm (or even ¼") farmer johns are flooding the market. For one neoprene doesn't age the best. Another is the cuts of material and even the materials were not that good back then. It was the best they had, which wasn't that good. There have been multiple generations of wetsuits since then. Materials that work better, fit better, more comfortable, etc. My current super stretchy 5mm modern suit is warmer and WAY more comfortable than the rigid 7mm 2-piece it replaced. If you don't know better the 7mm looks like a warmer suit. It is way more buoyant, you will get tired more fighting the springiness of the 7mm that does not like your arms anyplace except at your sides.
I am going to say that buying local is really good. Yes, used gear can be a good deal. But you have to really know what you are looking at. and as someone just starting in the sport that is something that you won't always know. Do the best research you can, when you buy used and it doesn't work out don't fight it. That was the cost of education.
