Im looking at purchasing an 02 GTP but my mechanic friends tell me to stay away from them because the superchargers have issues? are they right?

I have a 2000 park ave ultra 235000+ KM no problems barely any maintenance. Your mechanic doesnt like them because they do not make money off of them. One of the grestest lowest cost of ownership engines GM has ever created.

Only those not properly maintained. If the fluid was changed regularly, I did mine every 15K, then it will be fine. And the model year is not relevant from 99-02 as all superchargers in that year is the Eaton M90.
If the car ever had the supercharger pulley or nose drive modified, you can't be sure how long it will last but parts for the supercharger are inexpensive, better than stock, and easy to fix.

Remanufactured nose drive kits consisting of nose cone, drive pulley, lubricant,
sealant and coupler are available. The nose kits are an excellent alternative to replacing an
entire supercharger when dealing with low mileage bearing noise or leaky seal concerns.

This was from a service bulletin in June 2003.