I (and just about everyone else will agree) suggest strongly that you do in fact reflash a purchased n900 (or n810 or n800 for that matter)
That way you know as a certainty that you are dealing with a clean device and anything that occurs from that point on can be narrowed down to either:
A- hardware failure of some kind,
B- your own screw up...

This way you know for a fact you are not dealing with some past users screwing about ...
Why use someone else's configs?
their fcuk-ups?
goodness knows what issues the device may have...

Best to scrub her clean and reflash...

for example....(and conveniences sake...)
follow "the Perfect n900 Set Up"

http://wiki.maemo.org/N900_The_Perfect_Setup

as far as n900 repos go...the perfect set up is a bit outdated there...
there are other threads more current.