buick supercharger

ive got a great running 88 buick lesabre t type but it just isnt fast enough! im looking to cop a supercharger, but i dont have much experience w/ this. is there anyone who has done this out there?
ive seen the buick superchargers on ebay but im leary about getting a bad one. so again any help w/ ins and outs of this would be of great help!