Has anyone ever tried to book a round-trip ticket when you only need a one-way and then cancel your return leg because the round-trip was so much cheaper? Will you be penalized? I just need to get from Dayton to New Jersey...
Thanks
Sia

Go for it. The airlines frown on it but can't stop it. Think about it, how are they to know if you decided to drive back home with a friend or take a train or something like that. At least you intend to cancel your return so it at least frees the seat up for someone else on the return portion. Just don't do tell the airline you intend to do this.

Yes, you wlil be penalized if you TELL the airlines that you're changing your RT ticket to a one-way one. What you should do is just not show up/don't use the return leg.

Think about it. Suppose you broke your leg on a trip and couldn't make the return. Do you actually think the airlines would come after you because you didn't show up for the return? Just don't tell them you are planning to only use half of it.
This may seem dishonest, but let's use some common sense here. It hasn't cost the airlines a penny if you don't actually use half of your flight. In fact, they can make more money if they resell that seat.

... and keep an eye on the return flight. If it took off late (by a certain amount, not sure by how much, but it's a reasonable amount like 15 minutes or so) they have to give you a refund for the 2nd leg of the trip. Just tell them that the late departure no longer fit into your schedule.

A relative of mine was flying RT and while on vacation bought a car b/c he got a better price on it in the vacation area than he could back home, so he decided to drive home. The plane ended up being delayed so he got that half of his ticket price back.

You'll do everyone, including yourself, a favor if you call the airline once you've gotten to your destination and release the seat. Tell them you have to extend your stay indefinitely and ask, if you want, what the "penalty fee" would be for rescheduling the return leg. You never know, someday you might want to get from NJ to Dayton, and you'd have a ticket!