Definition of scalper:
(n) :
one who
scalps tickets to popular entertainment events: buying them in advance and then selling them (perhaps on the day and just outside the venue of the event) at inflated prices; a person on an open outcry exchange trading floor who buys and sells rapidly for his or her own account, aiming to buy from a seller and a little later sell to a buyer, making a small profit from the difference (roughly the amount of the bid/offer spread, or less)
"we could see three different scalpers moving through the crowd outside the arena, each muttering the characteristic refrain: "Need any tickets?""