Even being a dealer myself, used saws are more fun than new ones. I like taking a saw that was given up on and getting it going again. Most of the guys on this forum are more than capable of doing their own work, so used is no problem. Especially when you own several saws and it's not a big deal if one is down for a while. But believe me, that is not true of the general public. A majority of people are not even capable of general maintenance and they are often shopping for a new saw because they have ruined their current unit.
There are an awful lot of unwanted saws out there that people place little if any value on. There is no need to pay high, or get into bidding wars on e-bay. I agree with Mike's percentages on what to pay for used saws. If your not saving at least 30%-40% then you might as well get new. The best prices are on non-pro models of course. Lot's of stuff in the $100-$200 range. The best type of deal if you can find one is to get a pro saw that wasn't used professionally. Maybe a guy that bought a 372 to cut his firewood and no longer wants it. It will have relatively low hours on it, and if it wasn't abused, then getting it for 1/2 the price of a new one is a great deal.
But.........and this won't make sense at first, I won't sell used saws in the store. For one thing, I have new saws from $250 on up. For example, I have some leftover 350's that Husky found laying around. I sell them for $275, so how cheap would a used saw of similar size have to be? $150? And then I have to look at how much time I have in it. I can spend hour after hour messing with saws in the workshop at home. But at the store I'm naturally going to bill people for my time, and it's $60 per hour plus parts. And I would absolutely have to go through them pretty good to make sure they were OK, which brings up the last point. People naturally expect some kind of warranty buying from a dealer vs. a garage sale, so you have to make enough to cover something unexpected.
A quick story: Couple years ago I sold a used snowblower for a couple hundred bucks. In nice shape and ran great. I serviced it. Started up on the first or second pull every time. Turns out that the electric starter wasn't working, but I never checked it out. Customer wanted me to put a new starter on it, but the math on that didn't work for me at all. I'm not saying the customer's request was out of line, even at the great price he paid for the blower. But if he bought it at a garage sale, he sure wouldn't be going back to the guys house asking for a starter. I just put my cards on the table regarding the numbers and told him that I wouldn't buy him a new starter, but I'd gladly give him his money back on the snowblower, which is what we did. I just took the starter off the blower and sold it to someone else for the same price as the first guy, who wound up buying a new one. A happy ending for everybody, but it shows you how you can get bit with that stuff.