Always and Never
The first thing I explain to Product Owners when they're working with a development team for the first time is that there are two kinds of "never". There's the Business never, and then there's Developer Never. Developer Never is, of course, never. Never-never. Then there's Business Never, which really means "not more than once a month".
Slightly trickier is "always". It has the same problem of being far more precise in software than it is in English. What's worse is that it's often implied or inferred in an otherwise reasonable requirement. "The software will send an email when an order is placed." Is that an always statement? Does it mean Developer Always? Typical responses can be "Well, not if there's been a problem -- then we want to call." or "Yes, if they've given us an email address". Aha. Business Always.
In fairness, Business Never and Business Always are how people actually work in the real world. That said, this approach to Product Owner/Dev Team communication always helps avoid mistakes, and has never let me down. :)