Just a small but I think helpful thing that should be added is some sort of tag next to a players name that indicates they are learning a class they are not familiar with.

Like, we have the sprout which might tell us a player is new so we can prepare our selves to expect some mistakes. Being leveling naturally a level 80, your sprout goes away and therefore people may just assume you know what you are doing and are familiar with everything.

I know typing "Hey, never tanked/healed/DPS this before" can provide the same results, but I think a tag could be that much more helpful for those maybe more shy or forget to type out they are new with this job.