eBay

I AM TRYING TO GET A MESSAGE TO EBAY! IN THE CARIBBEAN, WE MUST HAVE INVOICES WHEN THE GOODS ARE SHIPPED IN THE USA. IT NEEDS INVOICES BEFORE IT CAN BE SHIPPED TO US. HOW DO I GET A MESSAGE TO SELLERS THAT WE NEED PROPER INVOICES?

I have never bought anything on Ebay before. I am in the process process of buying a few items. How do I know if these sellers are legit? I have a credit card, how do I make the purchase? Just give me any information that will ensure I don't get dupe...