One time sale item in billing automatically detects as service

One time sale item in billing automatically detects as service

if i have some items which i don't want to add in my "item" list because its sold only for one time.

but when i type item name in invoice, it (system) automatically takes it as a service and despite of HSN , it shows SAC code to be entered.

if its selectable i.e. either item or service , it would be very helpful and a must have feature.