Just normal wear, accelerated because it's always under load. The used cards are fine most of the time if the temperatures were stable under 80-90 degC. The ma

Just normal wear, accelerated because it's always under load. The used cards are fine most of the time if the temperatures were stable under 80-90 degC. The main cause of failure is the VRM, those components are the hottest, least reliable and least cooled. Sadly, sometimes a blown transistor or capacitor can take out the whole GPU.