Dustin,
I usually buy what I can see, so I get a lot from the shows. That way I can check it out first. I try to buy from reputable sellers such as Arizona Desert Ironwood, but it may boil down to having a different supplier for each type of material. Its inconvenient, but you will get better examples in each species in most cases.
You can look on some of the auction sites, but dont buy without photos. Lin