I regretted my very first (mtb) purchase, a 1991 Rockhopper, it was at least a size and a half too big (a 22" frame, I now ride an 18" Stumpy), and the bike shop I bought it from gave me no direction in sizing it. Since then I've been pleased with every purchase (I'm on my third mtb, and have a road bike in the mix now). That loss-leader of a purchase what back when really taught me to be meticulous and take my time.