control over more of the country's wrestlers, fewer independent wrestlers could publicly challenge the promoters' wrestlers to shoot matches. If an independent wrestler made a public challenge, the cartel wrestler could use his contractual obligations to his promoter as an excuse to refuse the challenge. Some promoters even used "policemen" to deter independent wrestlers from challenging their stars. These “policemen” were powerful wrestlers who lacked the charisma to become stars. The independent would be forced to face the “policeman” first, who would give the independent a vicious thrashing that would put fear in him and force him to spend a long time recovering. Promoters also had to deal with "double-crosses", wherein a wrestler who had agreed to throw a match instead actually fought and won, forcing the promoter to award him the title of champion for the sake of preserving the facade of sport. The promoters punished such wrestlers by blacklisting them. Blacklisting could be fatal for the wrestler's career, such was the dominance of the cartel. By the early 1930s, most wrestlers had adopted personas to generate public interest. These personas could broadly be characterized as either faces (likeable) or heels (villainous). Native Americans, cowboys, and English aristocrats were staple characters in the 1930s and 1940s. Wrestlers also often used some sort of gimmick, such as a signature move, eccentric mannerisms, or out-of-control behavior (in the case of heels). The matches could also be gimmicky, such as the wrestlers fighting in mud or in a pile of tomatoes. The most successful and enduring gimmick to emerge from the 1930s was tag-team matches. Promoters noticed that matches slowed down as the wrestlers in the ring tired, so they gave them partners to relieve them. It also gave heels another way to misbehave by double-teaming. Wrestling promoters struggled to find wrestlers who were both trained in authentic wrestling forms and had charisma. Towards the end of the 1930s, faced with declining revenues, promoters chose to focus on grooming wrestlers who, regardless of their skill, could draw crowds. By this time, most of the public knew and accepted that professional wrestling was performance art, so a background in authentic wrestling no longer mattered. After this time, matches became more outlandish and gimmicky, and any semblance professional wrestling had to catch wrestling faded. The personas of the wrestlers likewise grew more outlandish. Although the wrestlers no longer cared to make their mock combat