My best advice is to
1) if you are doing this online make sure to get clear unedited pictures with whites on. I've been to a lot of shows and stuff and the way something looks under super blue lights and/or in a picture does not equal how it will look in your tank. Do not trust a name.
2)make sure you are dealing with someone with a reputable history.
There's no substitute for dealing in person. I know alot of reefers have no other option, but since I'm fortunate enough to have reputable dealers, I'm not paying for something I can't see in person. If you can't then do everything in your power to vet whoever your dealing with.