I think you should not be up to the concert ticket price is $ 40 because you do that, it's tantamount to cheating. And of course, your friends must know that the final price is the actual price is much superior. I stick to what you do not want to cheat your friends, of course. So, I think if you were in trouble, but it should not be sold a ticket to sell more expensive, because in this way you will be faithful to you and your friends.