Basically, assume any item may be cursed when you try to equip it, especially good gear from lower level dungeons. Some cursed items can be fairly good or situationally useful once uncursed though.... so it's worth collecting and using even cursed equipment.
You'll be forced to switch "good characters" around a lot though, as they get ruined by curses until you can free them. I just lost my best Paladin last night, and it'll take maybe ~10-20 runs to free them. (Cursed to another class - was using PLD and a damage char to carry two useless characters through an easier dungeon to uncurse them.... Got stuck in a longer fight, PLD armor durability went to 0 - and it was game over for her. She was cursed and ruined before I could finish the fight. )