I've found a used Swarovski ATS at a decent price but I gather this is their older model...for about half that price I could get somehting like a Hawke Endurance with ED glass - brand new with lifetime warranty.
Hi,
used alpha scopes can be very nice - but please make sure to be able to inspect before you buy (or have a no questions asked returns policy) and know how to do it properly.
I have unfortunately seen lemons of from alpha brands which shouldn't have left the factory...
As for the ATS, its history is a bit confusing... It started out as ATS with normal glass, then there was an ED glass model called ATS HD, then they put the ATS HD optics into a magnesium alloy body and called it ATM and lastly, after the ATX came out and was a bit on the heavy side as compared to the ATM, they went back to an aluminum body and called it ATS again (but still with ED glass and it says ATS HD somewhere on the body).
So you should make sure that you get an ATS HD model and test it properly. Unless it's a hot day (ok, not too probable given your location and the date), you should be able to get a nice and sharp picture at the maximum magnification of 60 or 50x (depending on whether you have the newer and more desirable 25-50x wide angle zoom or not) and the best focus should be easy to find.
For a more thorough test you could make an artificial star (place aluminum foil on glass, make a very tiny and round hole with a needle and scotchtape in front of a led flashlight) and observe this with the scope from a distance of 30m or more. You should see a diffraction pattern called airy disc at best focus and when you defocus a tiny bit in each direction you should see equal patterns of concentric rings. See the following link for images of what to expect (ideally the aberration free aperture for the unobstructed case).
https://www.telescope-optics.net/star_testing_telescope.htm
Don't be too picky if you see a little bit of fuzziness on one side - a little bit of spherical aberration is common and will not be an issue at the relatively low magnifications of spotting scopes... unless you want to use the 1.6x extender.
Experienced astronomers who have star-tested hundreds of scopes tend to remember the handful of cases at best where the star test was perfect.
Astigmatism (ellipses vs. circles) and Coma (non-concentric patterns) tend to be more visible and should be avoided.
Joachim, who likes his 30 year old Kowa TSN-3 cherry very much...