Have I been lucky with my Karcher. I bought it about 10 years ago on offer for about £50 and I've had no problem.
Admittedly it only gets used 3 or 4 times a year and when I've finished I turn the water off and leave the trigger open until all water has been blown out of the system. It then went back in the garage, never a shed.
Prior to purchase I had been warned that leaving water in them, especially the cheaper models, would kill them. It would either cause oxidation/furring up of the aluminium parts used to reduce production costs or freeze if not correctly stored.
Colin