We're at a red light, there's a Corolla beside us, the tires catch my eye. They're Michelin X-Ice. It's only 19C (roughly 68F?), nice mid-May day. Ok, not so bad, a little late, maybe he's just thrown in the towel running them year 'round. Next red light we're beside him again: see the front tire has rotation arrow correct, rear going the wrong direction. The far side has gotta be a similar story.
I'm not sure, should look it up. I suspect the main issue is the tire would be much less effective, as far as traction goes. And that may come back to bite, when one sides gripping significantly better than the other. You know, my ears are burning a bit. Someone's started another thread in this forum, saying there's precious little positive in this posting. In hindsight I agree, sorry for the stinker. I'll hang out under the bridge for a while.
I doubt traction on dry roads would be a problem, but it sure could be in the rain. Plus, the softer rubber of Winter compound tires is going to wear much more quickly.
Had this on my Ford Mondeo: the official dealer put all 4 tires the wrong way round, causing the water to be funnelled to the middle of the tire. Noticed it when I started aquaplaning with just a little rain. Deadly dangerous. And the dealer couldn't care less when I told them to correct it. At such a time, I envy the American claim culture. Then at least you can hit them where it hurts. Safety for his clients was of zero interest to him. Maybe his wallet is something he cares more about.
I had similar issue at Costco. I went in with four loose steel rims/tires, to be replaced with (directional) X-Ice. It wasn't 'till I was at a gas station, airing them up more, that I noticed the buggers had sold me 3 rights and a left. It was a long day.
I've heard the arguement that people don't sue enough. Not to say there isn't any frivilous cases out there. The arguement is that many people that have an actual gripe don't speak up because they don't want to take the time or are simply too nice. So an offending practice that may have been stopped by hurting the offender in the wallet just continues. As to technicians putting unidirectional tires on in the wrong direction, they likely aren't the highest paid ones among the auto service industry. They might be a step above the ones at an oil change place. Which reminds me that I had to suck out over a quart oil after using my last free oil change at the dealer.