Again, I'll give people the benefit of the doubt here. Having a taxi wait for you has always been a fair request - with a big premium cost for doing so. Some people who do this with Uber may feel it's a perfectly legit request, knowing that the "meter is running", and may not think it's working against the driver at all.

This is a case where I genuinely hope the rider doesn't 1-star the driver for not wanting to sit around for 30 minutes at the grocery store. Just...summon another Uber when you're done shopping...