I think your idea of selling it at a 10% discount is hugely optimistic. At 4 months you’ve burned up a significant part of the factory warranty, and no one will implicitly trust that you maintained it properly, nor didn’t abuse it during break-in… I personally would not buy a machine from someone in your circumstances for just a 10% discount.
I'd go with this as well.
You'd get the 90% if it's hard to get an ATV and they're backordered forever and a day. That's been the market mostly recently. The problem is, that doesn't help the OP who wants to just pick one up for this winter - where's he going to get the super hard to get quad? Might get lucky - I don't count on being lucky in life.
Even on a 7k quad, I'd pay the extra 700 and get new/factory/warranty and be done - if I can. If I can't - it's unlikely that I'm going to find a used one, low miles/used 4 months total for sale anyway.
