Now that you have checked the VIN, and inspected the machine, what is a good price to pay? Check Kelly Blue Book, the asking price should be somewhere between Trade-In and Suggested Retail Value. Be sure to negotiate into the price any repairs you uncovered with the checklist.
If you do decide to buy or sell a used machine having a Bill of Sale for both parties is never a bad idea. Be sure to include the VIN number, year, make, model, odometer, and the signatures of both the buyer and the seller.