I buy online (in bulk) periodically and it's just fine. Just use a reputable place. I cannot speak to amazon, but condomania.com has a good selection, and I've had good service from them in the past.
Really it just depends upon how quickly you feel you will go through them as to whether or not to buy bulk. In my case I was giving quite a few away periodically for various reasons.
"Well, then," the Cat went on, "you see a dog growls when it's angry, and wags its tail when it's pleased. Now I growl when I'm pleased, and wag my tail when I'm angry. Therefore I'm mad."