Who to fire, someone who underperforms, or has questionable ethics?
I would fire both.
An underperforming rep that gets a pass just lowers the bar for everyone, unfortunately. No matter how nice they are. If it’s OK for Bob to always hit 30% of quota … then you just won’t have enough pressure and urgency on your sales team. You can’t have that.
You also can’t have ethical lapses on your sales team. Not only will that bite you later — and it will — but it will again encourage similar lapses in the rest of the team.
Both of these reps, in different ways, are toxic and detrimental to your success.