Javaid Ali's injury severed his carotid artery and caused massive blood loss and cardiac arrest.
As a result Mr Ali suffered severe and permanent brain damage and died on June 29 last year after his life support was switched off.
Lee Anderson, 31, denies murdering Mr Ali at his shop, the Sunshine Grocers, in Green Road, Paisley, on June 15 last year.
James Angus, 57, an employee of Mr Ali, told the High Court in Glasgow he sold cannabis from his van but not the shop.
He also gave customers tick and, at his death, was owed thousands of pounds, said Mr Angus.
Detective Sergeant Andrew said police had found 12 bags of herbal cannabis in Mr Ali's white van, which was parked outside the shop.
He said selling drugs was "a risky business" and agreed there was a danger of being robbed.
The trial before Judge Sean Murphy QC continues.