黄牛 (huángniú) scalper 

Usage:

“黄牛”是利用特有的和不正当的手段大量购买车票、门票,并以高价出售从而获得利益的人。
“黄牛” is someone who deliberately buys a large number of tickets in a specific and improper way and then sells them at a high price to make a profit.

Sentences:

1、Mǎibúdào piào de rén duì huángniú shì yòu’àiyòuhèn.
买不到票的人对黄牛是又爱又恨。
People who could not buy a ticket have a love-hate relationship with scalpers.

2、Chēpiào shímíngzhì shíshī yǐhòu, huángniú de shēngyì bùhǎo zuò le.
车票实名制实施以后,黄牛的生意不好做了。
After the implementation of the real-name ticket system, business for scalpers became terrible.

原文链接