You can't really usefully sell a provisional patent. The only person who can obtain a patent is the inventor. A provisional patent can only be converted to a full patent by the inventor. Unless the sale includes an iron clad contract with the inventor (the actual person), that the inventor will proceed to patent the invention and then assign it to the purchaser the "sale" of the provisional patent is almost worthless. If the guys want to go to grad school they might not be all that interested in the addtional work. (Although the innovatine work is already done in the provisional filing, the attorney's work is still to come. That of course is the expensive bit. As is the cost of the full patent filing.)
The filing of the provisional patent means no-one else can patent the same idea. What is sold is thus probably a guarantee that the inventor cannot go forward and patent it unless they assign it to the purchaser, or that the provisional patent will be allowed to lapse, in which case the idea becomes henceforth unpatenable. Something which might arguably be a worthwhile thing anyway.
None of this changes the fact that patenting business methods is just plain silly.