I feel ya, amigo. I can't tell you how many times my friends have tried to set me up with someone they knew and when I met them I felt like saying "What in hell were you thinking?!" And they would give me sh*t about it later saying things like "You barely know her" or "You're judging a book by its cover" or "You didn't give her a chance" or some touchy-feely crap like that. Well, IMHO if I don't get a good vibe from someone in a few hours, it's not going to get much better. Mind you, this has nothing to do with shyness. Even a shy girl exhibits her qualities, good or bad.
Now here's a funny yet pathetic story. A while ago, I tried eHarmony.com (or rather eDischord.com). After spending a ton of time going through their personality profile, it basically told me that there wasn't anyone in my area that I was compatible with. Doh! I expanded my search radius. Still nothing. I expanded it to the entire U.S. Nada. Ultimately, I shelved the idea for a few weeks (a good policy to live by when it comes to relationships). Then I got an e-mail "You've got new matches!" When I read about them, I once again felt like saying "What in hell are you people thinking?!"
Bottom line: YOU are the only one who knows who's right for you. Don't lower your standards. If you do so, you'll only end up resenting that person's incompatibilities. Of course if you have "Must be a Vicki's Secret catalog model" on your list, you might want to check your reality dipstick.
Still, there are things that should be standards and things that should be taken with a grain of salt. Compatiblities is a better term. If she's a very religious person and you're not or you're of a very different faith, that can be a big problem. If you're a home-body and she's a party-animal, that can be a problem. If she smokes and you don't, that's something that can be worked out. If there are activities that she likes that you aren't into, that's not necessarily an incompatibility. Being able to spend some time apart to do different things is healthy.