Whatever you buy, realize that you really should have it serviced before taking it on more than a pool dive. If you purhase it from a trusted friend or LDS who tell you it has been recently serviced then maybe not but otherwise you have no idea what the condition of the internals of the reg are. If it comes off of Craighslist or Ebay this becomes a must. I am not suggesting that buying used is a bad idea, far from it as long as the price is right but if you buy used you owe it to yourself to have it checked before using it in conditions more demanding than a pool. To that end, plan on spending another $100-150 getting the reg serviced and figure that into your price. Buying a quality used reg for the right price is often a great way to get a reg but spending almost new price on a lower end reg then having to spend another $100 getting it serviced does not make sence when you could have bought the reg new for another $50. Also, make sure the reg is still servicable. Scubapros are pretty much all servicable, many Aqualung (US Divers) and Mares are servicable although some models are not. Also avoid off brand or less common brands because service is no longer available or it can be hard to find a dealer. Finally, your reg will need to be serviced at some interval, I will not get into the "how often "debate but sooner or later it will need service. The recommended interval is between 1 and 2 years depending on the brand. You need to take this into consideration as well. If you don't have a local shop that services the brand you purchased, you will be forced to ship it off somewhere. There are good mail service shops (I can put you on a very good one) but that would add to hassel of getting it serviced.
Nothing wrong at all with a used reg, just make sure the price is a good one, taking into consideration servicing and convience of getting that service.
