I don't know how tricky they can be these days. I was at the local tyre place (and I live in a tiny country town, so it's not the latest and greatest gear) and he showed me how the balancing is done. He puts the wheel on the machine and locks it into place, presses a button on the machine. The wheel spins a few times, it then stops the rotation, telling the guy to place so many grams of weight on the inside or outside of the rim at a certain location and the job's done. Tested it - perfect - go to the next wheel. Under a minute, I'm sure if he wasn't explaining shit to me, he could have done two wheels inside a minute, or all four before I could have gotten a coffee from the vending machine.