To "turn away" business or customers means to say "no" and not serve them or sell them things. A company might "turn away business" because they already have enough customers, because it's time for a store to close, or because they have some disagreement with certain customers.
You can use "turn away" with other words as well:
turn away gifts
turn away people
turn away advertisers
When you use "it", "them", "us", etc. with "turn away", "away" comes at the end:
We had to turn them away.