Years ago I worked in some high-end audio shops and seeing how many hours the demo equipment was powered up and being used, I've stayed away from purchasing any of that sort of equipment.
I also tend to stay away from pre-owned speakers, even from individuals, as it's difficult to audition them and determine if they've been abused. Having said that, I've been successful in purchasing pre-owned electronics, when the models are in current production and are available for purchase as new, as it seems that it's more difficult to abuse electronics compared to abusing speakers.
I only have a power amp that I purchased used, from a seller who provided me the original purchase receipt, about four months after he made the original purchase from an authorized dealer.