If you choose to refuse a deal, you actually state that the deal has not gone through for a specific reason. You can edit those reasons under Settings > Preferences > Manage deal loss reasons. Refused deals are also taken into account in the stats.
Deleting a deal is irrevocable. You cannot retrieve it and it is not taken into account in the stats. It's better to only delete a deal if you're sure that there has been a mistake.
Customer support service by UserEcho