Who makes the turbo kit? A well maintained turbo should last 100,000 miles or more.

Few ways to find out relative projected reliability:

1) How much CFM is the turbo capable of, and how much was he running?
2) Who makes the kit
3) Did he have a turbo timer
4) How many miles did he run the kit

The intercooler is a good sign as the cooler charge is less stressful on the turbo's thrust bearings.