I can't agree with Duanob on used printers. Most old business printers are disposed of because they require maintenance which affects print quality or to be replaced by a faster model or end of lease. Companies specialise in fixing and reselling, that's where the e-waste goes. Decent workgroup or production grade printers are fully rebuildable and for the right models parts are plentiful.
Whatever you go for new or used if it's a laser make sure the fuser is easily accessible. It only takes one paper jam to burn a tiny amount of toner on to it, then over time it builds up and badly affects the print quality. Fusers can take between 1 and 90 minutes to replace, some can even be repaired for £7 to £14. Also check if the drum is built into the toner cartridge, if not check how much they cost and how easy they are to replace, they are a consumable.