I understand that logic is hard, which is why we endeavour to be as clear as possible with our updates. We even have a pretty flowchart on our delivery and returns policy for people that don't like to read: https://openrigs.com/information/information&information_id=6
That is a pretty flowchart!
Maybe you should add a series of pop-up boxes when a US customer is selecting surface mail as their shipping option.
"Are you sure? This could take more than 6 weeks to be delivered to you!"
Then if they click yes, have one more.
"I noticed your address is from the USA. 6 weeks is 42 days, and it might take even longer than that. Just to SHIP. This doesn't factor in fabrication time and customs checks. "
Then if they click yes again.
"Alright, shipping via Surface Mail. Your package should arrive within 2-3 months. Don't complain. You chose this method."
"Are you sure?"
"Are you sure you're sure?"
"I don't believe you're sure...are you 100%?"
"Ok just to check you're 100% sure, what's the square root of -37.517? In your head, no calculators!"