@katka They are unfortunately easy to break, but they also relatively easily repairable when broken. Thankfully, most chips on them have modern replacements (some are recent development; there's now a 6502-to-6510 converter, and people are developping FPGA-based replacements for the CIA and VIC-II chips).

If you get one, be careful of static discharge on the controller ports, and if it has the original power supply test the voltage on the AC and DC pins because they are notorious for frying the computer when they fail (you can mitigate with an inline "C64 Saver", but I'd just recommend replacing the power supply with something modern).