Can't comment on the scope issue, yet, myself, but the price seems a tad high, even for a minty one, depending on model. IIRC, last time I looked, the 5.5" "standard" models could be found for about $275 around here, with the campers a bit cheaper (only difference between the two is the standard's have flats milled on the bbl). Assuming it's the standard, and you can't talk him down any, I'd probably elect for spending the couple of extra bucks on a new one - especially if doesn't come with the factory box, manual, extra mag (I think they currently come w/ 2, at least), etc. The newer ones also have two "ears" on the back of the slide to aid with cocking - if this is an older one that doesn't, that is worth the extra $$$ alone.
I got mine about 3 years back for $175 used - not exactly "minty", but not abused and functionally just fine, and passed up another for the same price I saw a couple of weeks later in similar condition, so I don't think I got an unheard of deal on mine. However, they've seen to have gone up a bit since - I also notice they seem to be getting more prominent and gaining ground on the rugers, popularity-wise. The two are probably not unrelated. Anyway, definitely one of the most fun guns I have, for the $$$.
If you plan on doing a scoped target gun, you may want to look at some of the factory configurations for such - they have a couple of HB models w/ full length scope rails included. They are more espensive, of course, and aside from the barrel and an adjustable overtravel screw on the trigger (I don't think the trigger pull itself is adjustable), I don't think there is anything else different.
I'd suggest asking any buckmark-specific questions here www.rimfirecentral.com/forums/forumdisplay.php?f=17
, and especially pay attention to posts by a user by the name of chim. He has quite a few buckmarks himself, and seems to know what he is talking about.
Excellent, excellent pistol, though. I picked up an extra 4" bbl from the Micro model (another good thing - bbl swaps can be done in about 60 seconds) and had it threaded for an Outback II can - and now it is even more fun to shoot!