Demo usually implies one year old and not used too extensively. Solid state components like a power conditioner shouldn't be a problem and should be fine even if two years old. However, I'm more cautious for anything over two years and anything more than a year old with moving parts more like a turntable, CD, speakers, or TV. It's like buying a used car so amount of use is an important consideration. Finally, be cautious about 10+ year stuff. Classic amps, reel to reel, etc, are going to need refurbishing (belts, lubrications, capaciters, whatever). Most of my gear is used and demo carefully chosen for age/price. However, anything with a motor I buy new or no more than one year old. Equipment older than two years runs risking extra money to update/repair which might eat up your original "savings". Finally, used cables (IC, power, speaker) are often the best buys and get borken in for you too. Good luck.