You can't possibly shop for a used bike without knowing exactly what fits you. I am 6'1" with a 34" leg length (stocking feet, back to wall, book pressed upward to pubic bone, mark wall, measure up from floor), which makes my proportions in the standard range. I can fit a 58cm frame up to a 61cm frame, but must adjust stem reach and seat height accordingly. My top tube length plus stem reach length must equal approximately 68.5 cm for proper fit, although there can be some fudging depending on bar type and brake lever placement.

If you're 6' but have only 30" inseam, you would have a longer torso than average. You'd want to be very conscious about top tube length and stem reach to fit yourself. This might drive you to larger frames with shorter stems, but might not, depending on the frame geometry. Your real inseam measurement (from a bike fit perspective, not a pants rack perspective) may be longer than you realize.

Take some accurate measurements then begin looking again. Your local bike shop should permit you to ride a few bikes in your size, but it's best to be up front with them about your budget and what you intend to purchase. That way, they'll know that they're investing in you for future business, but not likely the sale of the bike that you test ride.

Phil G.