The letter said Mr Hawker had personally benefited from the misrepresentation because it increased the commission he made on the deal.
The letter also said Mr Hawker had inflated the price of another BMW X5 which a customer had sold to the dealership to buy a Range Rover from elsewhere.
The allegations were made while Mr Hawker was on notice for poor documentation, after BMW Financial Services raised concerns over "repeated omissions, inaccuracies, misunderstandings and failures to follow process over time".
Mr Hawker was suspended on March 21 and was told he would be dismissed for serious misconduct two days later.
He was asked if he wished to resign instead and he did.
He raised a personal grievance in April, claiming constructive dismissal and seeking $20,000 compensation through the Employment Relations Authority.
Mr Hawker argued the investigation into his conduct was carried out with undue haste, the dealership did not give him information relating to his potential dismissal, and he was not given a proper chance to respond to claims over the Range Rover invoice.
He said his actions did not amount to serious misconduct because there was no loss to any party, the financial benefit he received was very limited, he was under "considerable pressure from management" to push deals through, and the "creative means" he used to do so were within industry norms.
Mr Gibson had on previous occasions consented to similar deals, and had placed too much weight on the breakdown of the relationship with BMW Financial Services in the decision to dismiss him.
Employment Relations Authority member Kenneth Anderson found a fair and reasonable employer would have dismissed Mr Hawker on the grounds that his conduct deeply impaired or destroyed the basic trust essential to an employment relationship.
He found his dismissal was justifiable procedurally and substantively. A decision on costs was reserved.
