Yea I am also going to oppose the masses here. *If* I can tell the rest of the bike has been properly cared for, then buying a bike with fully shagged tires is my *ideal* situation. Then I get to pull them off right away with no guilt and put on my preferred tires of choice right away.
Buying a bike with brand new tires sucks if you don't like those tires. Sure it presents well and looks a lot nicer, but...my argument remains. I've got a friend that bought a 2010 Zx6r from a dealer, it had really worn dunlops on it...he didn't care, he was planning to put put Michelin pp3's on. He didn't even mention the tires as a point of negotiation. When he went to pick it up, the dealer had gone and put some brand new Pirelli Angel's on, which is more of a touring tire. So now he's riding around on tires he doesn't really like, counting down the mileage till he gets to swap to something else preferable. Because he doesn't want to pull off brand new tires.
So like I said, it really depends on the rest of the bike, but dead tires definitely isn't a scare factor for me on a bike purchase.
Good point. I would want to see good enough tires test ride or ride home safely, other than that, yeah, I'd rather buy a set.