First and foremost, check your state laws regarding private sales. I live in Texas and currently there are no restrictions on private sales (such as documentation.) It is, however, a violation of federal law if you KNOWINGLY sell a firearm to someone who can't legally buy it. That becomes the tricky part...if Ohio doesn't have documentation requirements, then you can simply ask the buyer, or you can ask to see a driver's license or CHL (which establishes age and residency...but doesn't rule out felony status, or other prohibitions on handgun ownership). If you ask, and the buyer states he can legally buy the gun, then unless there is some other indication that any reasonable person should have recognized (like, the buyer was obviously a child) you should be free of any legal concerns.
Some ask buyers to sign a bill of sale, which the seller retains. One thing that will really protect you is to have the transfer done by a local FFL...some will do it for a fee ($25 or so) and the buyer will have to complete a 4473, so there is not only a record but an approval of purchase, should a later issue arise.
As for the gun itself, you should be totally honest...disclose the actual status of the gun, rounds fired, any known problems, etc. My rule of thumb is that I tell a buyer anything I would want to know if I was buying the gun. To a certain extent, though, a buyer should research and know what he is buying, such as features of the gun (caliber, action, mag disconnect safeties, mag capacity, and so on) so that isn't so much your responsibility as it is to discuss your specific gun.
You can research prices of your gun in your area by checking Gun Broker. You can also trade the gun for the LC9, but you won't get as much for your gun in a trade as you will by selling it outright and then buying the LC9. Trading the gun does take care of any sales or documentation requirements, so that is one consideration. Your dealer may offer you a fair trade, if you take it to the shop where you bought it and you get the LC9 there as well.
Another thing to consider: offer the gun for trade on this website; or check into local Facebook groups. There are several FB groups in my area, and there are guns listed routinely on them for sale or trade. Someone may be willing to trade you even, or give you some cash plus a LC9.