If buyer is an L.L.C. in Missouri, would there be risks to the seller?

Nothing inherently wrong. The risks are that the seller doesn't know who he is dealing with, or even if the LLC exists, with other risks that have nothing to do with that. Don't do any real estate contract without a lawyer.

... would there be risks to the seller?

There are risks in any transaction. The specific risk here is that the LLC might breach the contract in some way. In such case, the buyer wouldn't be able to sue anybody but the LLC (which may be judgment-proof).

As Joypulv suggested, the contract should be drafted by an attorney. Make sure it requires the buyer to keep the property insured.