I made a small fortune doing this. You have to know the market where the shows are at to attempt to maximize your profit. The hard to get tickets to sold out shows obviously are the best. But they have to be great seats and not just any seats.
One of the biggest amounts I made was Shakira ticket in Miami. People paid way too much for tickets but, their money became my money. I did most of my sales via E-Bay 1 day sales before they changed their fee policies. It's likely not worth it now because you pay a hefty premium.
GNR will be easy to get tickets. I wouldn't even mess with that.
Now if you are serious, you buy NFL tickets. Tickets for games that have appeal. Example Dallas or Green Bay playing at Arizona. Those you can make bucks on. I know people that buy season tickets, sell those type of games, watch them on TV and the rest of their season tickets are paid for off two high profile teams/games. Especially Monday Night big games.
You'll need a good bankroll and be willing to take some losses if it doesn't go well. But if you stick to marquee hard to get, you can do well. Just remember not everything is as big as it's made out to be.
Good luck.