yep, the main one being to try them on before you buy them.
I did try on some specialized ones but I didn't like them - they had an annoying 'ridge' where the arch of your foot is, and I've got fairly flat feet so it dug in a bit. I do like the specialized shoes I've already got though. So you never can tell really, from a picture on the internet. You do get a better range online, and you could keep ordering different ones and sending them back if you don't like them, or if they're the wrong size, but that's going to be a fairly tortuous process that you'd have to be quite patient to do.
I did eventually settle on some scott shoes from another LBS, they were £40 and I'm pleased with them, they're comfy and look pretty mean in silver, and have got good ventage as summer's coming up.