Personally, I wouldn't buy a used ATV. There's just too many people that neglect maintenance on them. But if I were to purchase a used one, the miles on the ATV are not all that important. I would rather buy an ATV with 20,000 "driving around town" miles than one with 1,000 miles of wallowing in the mud or being used on a farm. Check the frame for paint chipping off the welds, which may indicate a rollover or lots of jumping. If you look into a Can-am, check for dents in the lower frame spar- if you find any, you'll need to modify the frame or replace it to avoid serious damage.
When you go to look at one, insist on taking a wrench and loosening up the oil plug to check for water which will be at the bottom of the crankcase. If you find water, it could be from a serious dunking or an engine problem. Also remove some plastic to check for excessive mud, if it spent a bunch of time in a mud pit it's nearly impossible to hide.
Sure a plow adds wear and tear, but that would be the least of my concerns. I would be far more concerned about the maintenance that was done. Here's a trick for you. I use this when searching for a used truck or SUV also, and it works best on private sellers. Ask them how much it can pull and how fast it can go. 9 times out of 10 they will start bragging about the big load they pulled and how fast theirs is compared to someone else's. You can decide from there after they get done telling their stories. Good luck.
