Surprisingly, interest rates are often negotiable. You'll need to have a good payment record to back up your request. It also helps to have an offer from a competing company with a lower rate that you can use as leverage. But it's worth a try. A phone call is all you're risking.
Cash advances are especially prone to 'special charges'.
Beside the fee, you'll be charged interest from the day of the cash advance. One other area is not misleading, but sure is expensive. Many banks push their cards by promoting the low monthly minimum payments. What that means is that you owe them more money and are accruing interest charges on a greater amount. The more you borrow, the more they make.