@madspeed rough morning? Lol
First, welcome to stangnet!
Now let's get down to business..
Let's start with some theory first, the supercharger is belt driven from the engine and is nothing more than an air compressor. This can increase the efficiency of the engine and provide better fuel economy providing that you can keep your foot out of the accelerator. Let's be honest though, boost is and will forever be awesome and there is not much chance of anyone staying out of the throttle.
As madspeed said, 118k is not high milage for these cars. I have had several customers buy blower kits and have them installed close to or over the 200k mark and not so much as a hiccup. I would look to see the owner having receipts at the very least and that the install is done cleanly. Are there other aftermarket parts on the car? Do you know which supercharger it has installed currently?