Choosing Will Ship Worldwide will tell a customer to contact the seller for costs.
You can use the "Will Ship Worldwide" option, but it works better if you use -> Shipping Details->International Shipping->Choose Custom Location-> and then choose from the menu.
Do NOT choose North and South America because that will over ride your USA pricing with the much higher international rate.
I would also suggest that you not choose notoriously terrible destinations like Mexico, Brazil, China, or Russia. Let those be part of Will Ship Worldwide, which asks the customer to ask you for a shipping quote. You can then add a premium to the postal rates as insurance against late delivery, loss or damage in transit, and scam buyers.
Most buyers are honest, but there are too many problems, most of them systematic, with shipping to those nations.