Solicitation: Selling mineral rights? Legit?

Hello,

I have a small interest in a La Salle property. I receive a number of letters offering to purchase the mineral rights but have ignored them. I received one that I am interested in with a flat dollar offer. They includes a pre filled Mineral and Royalty Conveyance document. Spoke to them today and they said they would be willing to send a check upon proof of notary of the document, then I should send mine. How do people do this when there is a potential to be scammed in this process? What steps should I be doing to protect myself from this type of transaction other than doing an escrow etc. Seems like so much risk for me. Thank you for your input.