Originally posted on 07/03/2017:
You sound like you understand correctly.
The fees should be 15-30 cents per transaction. Some people here say they have been using $1+ as they think it will ensure a faster transfer during peak periods. I have not found this to be needed myself. 50 cents is probably the most I have paid.
There is a formula based on the physical size of the transaction that doesn't make a lot of intuitive sense to the new user.
Easy rule of thumb is use double what the blockchain.info/wallet suggests as the fee.
I have no idea why you sent $13 for a $9.95 charge but you must have chosen to send that amount? Or made the fee very high manually maybe? Or maybe there was state tax on the 9.95?
No one else has mentioned being charged anything unexpected before.