Modern gaming machines use computer technology to operate their functions. Slot machine outcomes are determined unsing a Random Number Generator (RNG) which is a mathematically-based program that selects groups of numbers to determine which symbols are selected to produce a winning or losing outcome.
The truth is, yes casinos can control a slot machine or rig it only to give players small wins. Some casinos work with developers to create exclusive games. This gives them even more access to a game's code and RNG.