IMO, the only thing to look out for is that they are so much fun to shoot that they can be addicting. I got very lucky and stumbled on a used 617 at a small gun shop 1/2 mile from work. Because that shop mainly specializes in 9mm and 40 caliber Highpoints, it sat unloved and unwanted for over 2 months in the used showcase. OTD with red dot scope, mounting rail, rug, a brick of 22LR, and one speed loader was 506 and change. The last 3 weekends have been spent shooting it at a nearby 50 yard indoor range and I've managed to get my grouping down to a touch under 3 inches for a 12 shot string at that distance from a bench rest. Would have been 2 inches if it weren't for the 2 flyers.
As for the model 17 and 18's, I actually prefer the look of the partial lug barrel over the full lug on the 617. I got my 617 simply because it was all I could find and I happened on what I believe was a real bargain. I also prefer less weight in the muzzle because I can shoot better in rapid fire DA with a lighter barreled gun. So, I've been eyeing listings for the model 17 and 18. Can't afford one at this time but I do keep looking.
Good news is that the distributor Davidson's is listing a inventory 99+ of their "special feature" model 17 and quantity of 18 of the model 18 at this time and 99+ of the "special feature" model 18. Based on the list price, I would expect that a local dealer rep for Davidson's will probably sell one to you in the range of 775 to 825 dollars. However, make sure you shop around at you local dealer reps for Davidson's because they can vary widely in what they charge. When I decided to purchase my 610, it was through Sports South and one dealer wanted 875 for the 610 while the other charged only 775 for the same gun. I've also found that I get a better deal on guns by paying cash because it saves the dealer the cost of the credit card fees. As for timing, I ordered that 610 last Labor Day weekend and had it in my hands the following Thursday. Which is why I like to watch the distributor's web sites, it makes ordering something that's in stock at a distributor a very pleasent experience as opposed to waiting 6 months to a year for a factory order. Following are link to Davidson's and Sports South and both have dealer listings by state and zip code you can search.
Sports South. BTW, they could learn a thing or two from Davidson's Gun Genie because you'll have to scroll thru the entire S&W handgun list to find the model 17 and see if it's in stock. They also don't show the number in inventory, only if it's in stock or not. However, they did ship that 610 out very quickly and they are the only distributor I know of that stocks the 610.
Online Catalog
Davidson's. I just love the Gun Genie, it makes it so much simpler to look for a specific model. Haven't yet ordered from them yet but have heard good things about them from one local dealer who is a rep.
GalleryofGuns.com - Gun Genie
Davidson's 22 revolver listing.
GalleryofGuns.com - Gun Genie
As for used prices on a model 17, that is going to be completely dependent on Condition. In my area a real beater will command at least 300 dollars and after that the prices go up quickly. In addition, they are such sought after guns that for a really nice condition model 17 you'll probably pay nearly as much for one that is brand new. However, you could always get lucky like I did with my 617 and find one sitting in an area where people turn their noses up at a measly 22 caliber revolver. My best guess on price range for a used 17 would be between 300 and 700 dollars.
As for what to look out for, about the only things that I think can do any harm to any of the steel S&W 22 caliber revolvers are shooting into a squib, dry firing it empty, or a LOT of really hard charging rapid fire drills, plus rust for the mild steel models. I carry a Streamlight Stylus LED flashlight that is about the size of a pencil and these are fantasic for doing a barrel check. Any bulge due to a squib being shot into will show up readily as you peep the barrel as a dark band at one point. Because the bore is so small for the 22, pitting from rust will be difficult to see so take some readers and look carefully. In addition, the barrel will have to be well cleaned in order to see any minor pitting from rusting in the barrel. BTW, I don't think minor pitting is an issue beyond the slight increase in leading it may cause. As for wear from rapid fire practice, or damage from dry firing, these are things that can be repaired, in some cases rather inexpensively, worst case you have to pay to have a new cylinder fitted in addition to the other parts it may need. So, if you find a model 17 that's quite cheap due to wear or minor damage, research the cost for repair and make your decision based on that. BTW, I have seen many posts that indicate that a slight bulge in the barrel of a model 17 due to a squib being shot into has no discernable effect on accuracy. So, if you find a squib shot 17 it at least deserves a test drive, while it will kill the resale value it will probably be an excellent bargain shooter.
One final note. Prices for these guns may seem a bit high considering that they are 22 caliber guns. However, keep in mind that they are guns that will easily last for well over 100 years with some basic care. In addition, they are VERY cheap to shoot. In the long run, it's hard to find a better value even if the buy in price does seem a bit high. IMO, anyone who shoots a wheelgun should have at least one 22 revolver and I think that you'll find that every one who has at least one agrees, and is probably looking for another. Me, I would really like a model 18 and a 5 inch model 63, what you'll desire after you have your first will probably be different. Consider this a warning, just like a certain potato chip, you can't just have one. I have to limit how much 22LR I take on a range trip because it's so much fun to shoot that on some days I wouldn't shoot my major calibers.