If you want average (mediocre) work, ask for it. Be really clear up front that you want something beyond reproach, that's in the middle of the road, that will cause no controversy and will echo your competition. It'll save everyone a lot of time.
On the other hand, if you want great work, you'll need to embrace some simple facts:
It's going to offend someone. If it doesn't offend them, then it will make them nervous. The Vietnam Vets memorial offended a lot of people. The design of Google made plenty of people nervous. Great work from a design team means new work, refreshing and remarkable and bit scary.
If you want something great, you've got to be prepared to protect it and defend it. Come back too many times for one little compromise, and you'll make it clear that average was what you wanted all along.
You can't tell me you'll know it when you see it. First, you won't. Second, it wastes too much time. Instead, you'll need to have the patience to invest twenty minutes in accurately describing the strategy. That means you need to be abstract (what is this work trying to accomplish), resistant to pleasing everyone (it needs to do this, this and that), and willing, if the work meets your strategic goal, to embrace it even if it's not to your taste.
Read the full post here: How to live happily with a great designer.