You need to find a jeweler you can trust - whether it's online or local. When I've purchased rocks for DW, it was always in person from the local jeweler I purchased her engagement ring from 30+ years ago...because I trusted them.
It's more than simply about the best (perceived) bang for the buck. You need to be confident about what you're purchasing, that it is what you're being told it is, because that's how they're going to price it, and most of us are not experts when it comes to gemstones. I don't know that I could purchase diamonds online. You might see the picture online, but colors have a tendency of not being exact when displayed on a monitor for one reason or another. I want to see it in person, be able to take it back if there is an issue, talk with someone in person, and again, trust the person I am dealing with. I just could not see myself getting comfortable with it online.