Quick answer: Most order issues come down to a few common mistakes, double check these when you add an item and you'll avoid most delays.
The most common causes of an Issue status
Incomplete delivery address
Missing size, color, or type
Item is out of stock
Listed price doesn't match the actual price
Shipping or taxes are higher than expected
Wrong currency selected
A couple of things that help
Partner Store items sync price and availability automatically, so they're less likely to cause issues. See "What's the difference between the Gift Store, Partner Stores, and Verified Stores?" to see which merchants are covered.
See "What should I include in my item's price?" for how to set prices that won't trigger a mismatch.