Inspect your party members before you enter dungeon and start the run?
Common red flags:
- Low item level
- Low M+ score
- Decent gear but no enchants
- Offspec Trinkets (i.e. Tanking trinket for DPS, Intellect trinket for Tank)
Also communicate as soon as you see a red flag. Ask (politely) what's going on with X red flag. If no answer or answer doesn't satisfy you, then leave prior to run starting.