Under Ohio's mitigation standards, a signed proposal comes before any work. It lists the Ohio license numbers, scope and completion date, chemical hazards, a compliance statement, homeowner maintenance, the price and yearly operating cost, and a guarantee statement.
More detail
The requirements live in the appendix to OAC 3701-69-08, the Ohio Radon Mitigation Standards. The guarantee line has two legitimate forms: a guarantee that the system will bring the average below 4 pCi/L, with its conditions, or a statement that there is no guarantee and why. An old stone foundation can honestly earn the second answer; a plain slab rarely should. If the company that tested the house is also proposing the fix, Ohio requires the contract to say so plainly and to state the advantages of long-term testing and the value of a second opinion. When the job is done you should receive the floor plan drawing, test data, warranties, operating instructions, steps to take if the alarm trips, the installer's license number, and the ODH radon program's phone number. See what a quote should contain, line by line.