I think shopping for a used quad depends on your market. Around here in Southern Ontario when I was looking, it seemed liked every used quad was going for (or at least were asking for) $6k+ for a 10 year old ATV. Meanwhile a brand new one was only $8k.
For me, it wasn't worth the risk to buy a 10 year old quad and who knows how it was treated for only $2k less, so I bought new and didn't look back. I bought a Kodiak 450 and it's been great. Nothing but oil changes so far.
I found about the same value retention in flatbed car hauler trailers when I was shopping for one of them. Used and abused prices were generally not much below off the lot new prices for a comparable trailer, so I bought off the lot new.
Yeah, for that kind of age/savings formula, def not worth dicking with used. But I shop USED!
Or, in the case of the stuff off Crown Assets, I take an acceptable level of risk based on who owned the stuff before me. RCMP usually takes pretty decent care of their stuff. Fer example.