Most of the online retailers are trustworthy in the sense that you’ll get what you pay for. However most are selling cheap crappy knockoffs of the Original or the Volcano. Plastic vaporizers are the worst, not only are they usually cheap crap, but they smell like burning plastic.
I’d suggest you figure out the model you want, and then go to the manufacturer website and find out who they have as dealers/stores. You might just go to a store and buy it, or direct from manufacturer. Usually that’s best because they’re the ones you want to deal with if there’s any problems with it.
Most of the knockoffs don’t do repairs, so be cautious about which one you settle on.
Youtube has some tutorials if you want to see them in action.

vaporwarehouse is the only online retailer that sells the Original, and they have a couple others. Volcano is sold a bunch of places, silver surfer and the dabuddah are ok, check with their websites.
The “globe” style aren’t worth having, and the ones on ebay suck.