You can google them and learn as much as if I did so I will not comment on that part. In general they could have made an error in their offer and will rescind it. They could be doing a bait and switch too. Send out a high, non binding offer just to get a conversation started. Did you contact and talk to all the companies that sent lower offers? Probably not. Sending a wow offer which the company then seeks to negotiate down is common. Roughly equivalent to the old pushy salesman foot in the door. I must also say there is a possibility that it is a genuine offer by a company that isn't bargain hunting. You can't make money off of minerals before you own them.
As for any company following through on a purchase? You need a solid contract, not what amounts to an option to buy for the buyer, Then, you have the right to sue as in any other business deal.
As long as my title wasn't clouded, I wouldn't sue if the other side backed out unless the amount I stood to gain in enforcing the contract was considerably more than I could get elsewhere, like more than $50,000 than I could get elsewhere. Lawsuits have aggravation/nuisance cost, to you.