A brief question on the protocol of selling is this group.

I placed a FS ad and had two responses, both of whom now want to but the product. I agreed to sell to the first person who specifically stated they wanted to buy it, but had another email later from someone, who responded to my post first, with the same request.

Which leads to my question, Is there a generally agreed upon protocol for selling here? Do you sell to the first person to clearly state they want to buy the product or wait for those who might have replied to the post earlier have an opportunity to buy?

I have a couple more pieces I will probably sell, so I want to be fair to any people who might responed.

TIA