Service without direct cost
When the owner performs a service without a separately recorded purchase cost, service revenue may contribute strongly to gross profit, while general expenses still affect net profit.
Outsourced service cost
If another technician or shop performs the work, record the genuine purchase or direct cost so the resale margin can be understood.
Mixed bills
A repair bill may include both a spare part and labour. Product quantity should affect stock; service quantity should not be blocked by product inventory rules.