Actually there are no real rules, but people tebd to agree to not want to see some specific stuff in duels. Those things mostly are said to be dishonorable and give a real advantage over the enemy. Thats why most people dont like following things in duels:
Cost poisons
Immo pots
Duroks bane
LOSing
Permacloak
In tournaments lots of rules are present, which also prohibit much more sets.
What rules do you follow in duels? (No shuffle, no shields, no sloads etc) If any!
What do you deem as dishonourable?
What do you think shows lack of sportsmanship?
What type of opponent do you think shows lack of skill and finesse?
What sets do you think people cheese with?
The only thing dishonourable in duels is to whine and gripe and hate-whisper and badmouth someone if 1) they reject your duel invite, or 2) they win.