i buy used when i can for all the reasons mentioned here. when i was really into audio years ago id buy 20 pieces or more a year and turn most of it and keep a few. along the way i discovered a few alarming realities with used gear ususally 10 yrs old or more. solid state devices evolve rapidly and supplers dont hold inventory so repairs can be imposible at times. there are many metal case T03 and darlignton type outputs transistors no longer available. levinson, rowland, spectral and many others have potted modules that are unrepairable, if the mfr doenst have one you're SOL. I had a Klyne preamp with bad relay, Stan didnt have anymore and the mfr stopped making them. it rendered my unit w/o the phase inversion and balanced capability i wanted. ive had same issues with early Krell (KSA/KMA fan-cooled series) and Classe (DR-2/DR-3) - essentialled rendering the units as doors stops or fancy paper weights.
CD transports have similar risks, i passed on a killer deal for reference transport, one-owner in mint cond. with boxes, papers, etc. later to find out the guy who bought it had problems 5-mos later and krell had no more replacements transport mechanisims nor did any NOS ones exisit. if you're lucky you can find a used pro version of the correct model on ebay and canabalize it - but you're just buying time at this point.
tube gear is much different, the circuits are inherently simple, just a collection of caps and resistors, save for maybe few SS regulators theres nothing that cant be fixed or substitued with other parts.
bottom line, its a good idea first to contact the manufacturer to see if they still support the model you're contemplating and if it contains any crucial devices that are in short supply or non-existent.