This an export transaction in which you are the "exporter of record" you have obligations to both the US and the importing country. There are required documents, as an example a Commercial Invoice and perhaps other documents. These documents are required for both the export and import side of the transaction. Some foreign buyers use a "Forwarding Agent" to manage all these requirements as well as arranging the actual shipment of the goods. The company you have been pointed to may be such a company or individual with both knowledge and authority to handle the transaction.
Now there is payment, the safest and simplest traction would be to sell the item to the guy in Miami have him pay you thru PayPal and let him deal with the process of getting it to the end buyer. You are paid and out of the loop. You don't own it anymore and you are not exporting it. He is. Take your money and forget about the rest.
Now, you may be asked to ship the goods to this guy in Florida with the promise that you will he paid by the end buyer. Problem here, is that you don't know what is going to trigger you getting paid. You also don't know who is going to pay the freight, handling and duty on the shipment, that could add up to some dollars you don't want to pay.
I have sold lots of stuff on Ebay with a few export sales. Every time it was an export I just "wrote it off" maybe I would get paid and maybe not. And maybe I would get a call from customs enforcement. I got lucky and never had a problem, but finally decided I would not do it anymore and excluded export sales from my listings.
You may just want to wait for a domestic buyer and not get dragged into this mess.