Given our litigious society, always looking for a scapegoat, I strongly recommend at the very least a handwritten bill of sale signed by both parties. You have to protect yourself and every bit of proof you have adds to that protection. If you have a reasonably current version of Outlook or some other word processor, you can print out a blank bill of sale template and hand-write in the details. If you're selling a gun, make sure you include the serial number and the purchaser's Ohio DL#. Then as someone noted earlier, if it does hit the fan later you can show the authorities that you did your due diligence and that will help avoid a lawsuit.
More details please. Having a bill of sale with a serial number and driver license number proves nothing. What it does do is it becomes a self confession that you did sell the item. Now prove you were not reckless; prove you did your do diligence.
So, how does a bill of sales protect you?
Bringing a civil suit is easy. Proving the elements of the suit is a different story.