white opal for a ring, is it a bad idea?

i'm looking into getting a white opal for a custom signet ring but i'm struggling to pick a stone. i've been watching a bunch of white opal auctions lately, but honestly, it's so hard to tell if the quality is actually good just from the photos and videos.

i know opal is soft, but what should i be looking for exactly so i don't get ripped off? how do you guys decide if a stone is worth it or not when buying online? any tips would be a huge help.