Stanley Bostich makes the best of all air powered nail guns and fastners.  Other makers include Porter-Cable, DeWalt, Paslode, Craftsman, and others.  Stanley uses magnesium frames and housings, strong lubrication points, and simple to replace O rings in construction of product.  Used items are thrifty, easy to clean, repair, or find items for locally.  Fastners are easly found at most hardwear or building supply stores.  External wear, scratches and mars, and signs of use do not usually reduce the effectiveness of the Bostich nailer.  A quality product that will out last several jobs and is dependable.  Average price for a used unit with or without a case is $60 to $110.00 or more.  New these units can cost $189.00 to $300.00 depending upon model and features.  Buy only the features you will need for the job to save the most money.