Most casinos are obliged to have an extensive array of security cameras and recorders which monitor and record all the action in a casino, which can be used to resolve some disputes. Some casinos use facial recognition software to detect known cheats and criminals.
However, the best way, in my opinion, is to stay at your machine and tell a slot attendant you would like to speak to a host as soon as possible. They are able to get the host your message by relaying it to a supervisor or by using their radio. Having a host meet you at your machine has several advantages.