I grew up where Iowa, Minnesota, and South Dakota cone together.

The thing is, they're not really offering to do your errand for you. They're noting that they could and asking if you want them to. And if you genuinely need it, you can then ask them to, but, and this is crucial, there's a cost. They'll be doing you a favor, and you will need to act like it, ideally by both apologizing for the trouble and repaying the favor at a later date.

It comes back to the idea of not asking people to do something unless you're reasonably sure they'll say yes. You can do this either by making gambits like the ones above to try to assess their preferences (polite) or by applying pressure (pushy). Because the only thing more rude than saying no to a request is putting someone else in a position where they have to say no to yours.