pimpin_civic said:
To my understanding, the entire winter-tire is made of a material that does not freeze up like regular all-seasons do.
Sorry, I think the way I structured my explanation may have caused some confusion.
First, you are correct - snow tires will be softer in cold weather than all-seasons.
However, for even better grip on ice, some snow/ice tires have a super-ultra soft compound that only makes up part of the tread, and it can wear very fast.
For example, Blizzaks have something called 'Multicell' compound which does not comprise the entire tire (I don't know what tires you are getting though, it may not apply to you). However, it is the Multicell compound that sticks to ice. Once that is worn away, the tire behaves like a normal snow tire.
You may want to google the specific tire the guy is offering and see if it too has a multicompound construction and whether it may have worn off the super-sticky rubber in the 2 seasons he's had them.
Heck, in the worst case you may be able to haggle down the price some more.
Good luck