It really depends on what you're looking for. Are out out for the best price, quality, a mix of both? Are you willing to wait longer for a better product at a lower price, or are you willing to pay more for that product to get it faster?
There are many, really great vendors. It just depends on what you're looking for. My favorite brand for batteries and set up extras is Volcano. I like the cigarette style. But a lot of other users don't like that company. They prefer something else. My favorite juice site is Pennys. But again, other users prefer something else. I know a lot of users really like Backwoods. It's more or less, subjective. And you will find people who hate one company, that others will love. Now there are a few bad places out there, that you, honestly, should not buy from. But a quick Google search involving "*Company* a scam?* will usually give you a pretty good idea of what's going on. There is also a Negative suppliers section on this site.
That is what I am afraid on, especially online. Is the "Scam" part. I am not rich, and can only make an underfunded, educated decision, LOL.