I am ready to pull the trigger on a Specialized Allez Comp from CL. The only problem is that the frame size is 52cm. I measure my inseam to be about 30.75" (I'm 5'7") and am afraid it might be too small. Otherwise it's perfect. I don't know how to determine whether it will be good enough or not and I don't want to drop $800 on a bike that won't fit at all. Suggestions?

If the seller is relatively closeby, request maybe doing a test ride? I am about the same as you, but I'm a little taller (5'9/5'10ish, 150 lbs), and I used to ride a 54 Allez, now a 54 Tarmac.

I was planning on doing that, but ultimately I wouldn't know what to look for in the few minutes I'd get to test it. I guess I'm better off going to an LBS.