My first pair of boots were used Vans BFB's with two days on them. Guy got them and realized he needed a wider boot.
They cost me $50 and I got about 100 days on them
Yeah, I'd be very wary of boots used more than 5 days... even then you don't really know if they're straight-up lying to your broke ass
Why this particular boot? Look around, there's gotta be better deals than that. Leave that shit to people who don't know any better.
I'd feel bad about selling anyone used boots at all, unless they're hardly ridden at all.