People like to see the words "FREE SHIPPING". I used to just eat shipping costs as part of doing business for ground as long as the product had a decent profit margin.
If the profit margin was tight or if they negotiated with me they paid for shipping on the invoice at 1.5 up to 5 times my cost depending on how annoyed they made me with their negotiations.
Anything other than Ground, customer always paid for shipping + 10% or gave me an account number.