Tabitha,
I bought a Premier about 6 years ago and just recently replaced it with an S200. I moved the Premier to a rent house and it is still working just fine.
Robots either work or they don't... Either the seller is willing to demonstrate it in his pool or not.. I would not buy it unless you can see it working. Often people that sell robots say that they moved and no longer have a pool.. ???
Premier robots have foam climbing rings that unless replaced will not last five years, so that would be one thing to check.. Not really a problem with gunite pools, but I would suspect they would be needed for a fiberglass pool. So you might factor that into your offer price.
All that said, the Premier is old and has a bottom basket... I like my $700 S200 much better...
Thanks,
Jim R.