I just went the Google route. But you can't research whether the source is legit online. All these guys are busy setting up fake accounts to praise their gear and call their rivals gear bunk. If the source site is only a middle-man between you and a UGL, you can check the UGL's website. They usually have a source-checker on there where you can enter the source you are curious about. All that will tell you, though, is that the UGL added the source to the list of trusted sources. It doesn't tell you what their criteria is. Maybe the source is run by someone at, or affiliated with the UGL, or maybe they just let any Tom, Dick or Harry sell gear on their behalf. Maybe the UGL removes any source from the list if they hear the source is selling bunk, maybe they don't, or maybe they never bother to police the whole affair.
Still, you can research if he UGL makes good gear easily enough, then, if they have a source-checker, and the source claiming to sell their gear checks out on it, I guess that's as confident as you can be. However, even if you hear of a good UGL, there will be knock-off websites with a similar name, so make sure you have the right one.
All that said, buying it online is still a gamble. But, once you have a source you can trust, all you have to worry about is customs seizures, or your source turning to the dark side, or the UGL turning to the dark side, or the UGL getting skanked with bad powder.