Looking at this a bit more broadly...
Anyone you sell to must be an Indiana resident. Ask to see a DL to verify. If someone who lives in another state wants to buy from you, you must transfer the gun [STRIKE]from an FFL in Indiana[/STRIKE], to an FFL in the buyer's home state and they must complete a background check.
If you know the buyer is a prohibited person you can't sell them the gun. If you don't have reason to believe they are prohibited then you are fine.
Some people prefer to ask the buyer to fill out a bill of sale so there's a paper trail showing you sold the gun, but that's not required. Others ask to see a buyer's LTCH since it means they completed a background check with the state at some point, but that's also not required.