"I then got threatened for trying to 'tell him what to do' when I told him he can't sell the car to the public," the customer claimed.
Watson said he was taking legal action against the customer for threats allegedly made against his business.
As he described it, the customer demanded the car - which had been reduced in price due to the defects - be removed from the yard.
He then refused to leave the premises despite being verbally trespassed.
"I escorted him off the yard without touching him," Watson said.
The customer then returned, this time recording on his phone.
The video shows Watson holding a piece of paper in the air, saying it was a trespass notice.
"Get off my yard," he repeatedly yells.
Meanwhile the customer tells him he has called police and they are on their way.
The video shows Watson walking the customer off the property with his arms extended, before the pair begin to tussle.
A second video shows the customer asking a friend to hold the camera as he follows Watson back towards the office, saying "listen to me".
"You've hit your worker, you've hit me," he says.
Watson walks back towards him yelling "f*** off my yard mate, alright?"
He then tries to walk away again, with the customer following. Two more people emerge and appear to be herding the man away, telling him he needs to leave.
"I am leaving," he replies, shortly before Watson walks to the office door and punches it, smashing the glass.
"That's your f****** head..., get the f*** off my yard now," he yells as a staff member pushes him back towards the office.
More of what he says is difficult to decipher, but includes the words "or I'll f***ing kill you".
The video ends with the customer being escorted off the yard by another person.
Watson said the customer had filmed him to "entrap" him.
He said his outburst "wasn't my finest hour".
"Yes, I hit a window instead of hitting him, which I thought was a far wiser thing to do at the time. I wasn't really thinking too fast."
Watson said he had surveillance footage showing the customer refusing to leave the yard, and had audio proof of phone calls he had made threatening staff and saying he would burn down the business.
He claimed he had video showing he initially asked the customer to leave the yard six or seven times.
"Every second phone call at the moment to my business is a threat of violence to either myself or my staff."
Watson declined to provide any video or audio to the Herald.
He was at the Botany Police Station this morning laying a complaint against the customer.
Watson said the assault allegations were "a whole lot of crap", and that the staff member he supposedly assaulted was his own wife, whom he "never touched".
When asked about threatening to kill the customer, Watson reiterated it was not his "finest hour".
"He had pushed me to the brink ... I was so angry.
"That recording shows a very small portion of what happened."
Police last night confirmed they received a report of an assault at an address on Great South Rd in Papatoetoe just before 2pm.
In a new statement, today police said they were called to an incident where threats were reportedly made.
"Police have not yet received a formal report in relation to this incident, however we will be making follow-up enquiries," a spokesman said.
