take it to RMP or somewhere to get checked out first...
Is there any info that says where it was serviced? (service records)
$13K for a M3 is a crazy good price... in fact a STEAL of a DEAL if its in good condition.
Think about it this way... i bought my 2003 325i for $10K with 135,000 km... so to get an M3 for $3k more... DANG!