I order directly from the manufacturer if I can. No problems there. I've also ordered perfume from places like Sephora. No problems there, either. I wouldn't buy perfume from someone on eBay though, or from an online seller that's "questionable." "Questionable" is different for everyone. You just have to go with your gut feeling.
It depends on how "off" your willing to take a chance w/ your scent being in order to save money- if its something' your going to wear often, then you prob you should just check out your local discount place otherwise, eh, the reliability is all chance really.