First, I do understand the liability. As a matter of fact I think this would decrease liability for a few reasons. 1. The 4th Amendment and other Constitutional rights are actually not binding on private businesses. Because of this expectations of privacy are GREATLY reduced. Yeah if without warning they look under a bathroom stall door or bust it open there might be an issue because for a tort violation of privacy against a private business that intrusion need be highly offensive to a reasonable person. An overly invasive search would also fall under this issue. However a business can set a rule for entry that says you must consent to a search, so long as the private security is not acting as an agent of the police and only for the purposes of deciding if you should be granted entry or if you should be ejected. Now the person is free to say "I do not consent to a search" and leave. If the security then detains the person and still goes in the person's pockets there may be an issue but the requirement of a search isn't an issue. What can also be issues are claims of discrimination or sexual harassment. Having female security personnel would reduced issues of the later and regarding the former, having proper training and consistent codified policies would go a long way to reducing liability in that regard. 2. Even if your security isn't armed having them with UoF training such as Pennsylvania's Act 235 would also go a long way to mitigating personal injury claims that result from one say a night clubs bouncers "escorting" a problem patron out. Now I concur with you that expense of training and paying employees with certifications is one of the issues that discourages businesses from these practices. As for theaters I can only speak to ones in Pennsylvania. Sometimes it is for specific movies. Example the Movie Tavern I saw Star Wars Episode 7 at had security that denied entry to fans wearing costumes that included masks or concealing makeup and search them to ensure they were not entering with concealed "costume" weapons and more than a couple theaters in Philadelphia (not in the nicest areas) have such security regularly /shrug.