Initially he was involved in circuit racing and then moved on to speedway racing, and became a "frequent flyer" client of the Brennans when it came to repairs and maintenance, he said.
Mr Guy said this was a highly specialised field and in those days there had been "very few" service providers in Tauranga that had the skills to do that work.
He believed Mr Brennan carried out all the work, as the accused was the person who discussed the repairs done with him, and Mrs Brennan was the front of shop person, he said.
Mr Guy said that, as well as being a client, he was also a close neighbour of the defendants.
In his evidence, Mr Clarkson told the court he had already secured neighbouring premises as part of the then planned multi-million dollar development in Gate Pa but the Brennans were proving difficult.
The tough negotiations were made public in a Bay of Plenty Times article, published on October 14, 1999, in which Mr Brennan was reported as saying they would be "staying put", the court was told.
Negotiations took several months and most of his dealings were with Grant Brennan, he said.
Mr Clarkson described Mr Brennan as being "very aggressive" in his financial dealings with him, but finally settled after being offered a "much higher price".
Mr Clarkson was asked about a letter sent to him in September 2002 by the Brennans, asking whether he was interested in being involved in their planned establishment of Brennan Racing Manufacturing Ltd.
He said he could not recall receiving this letter.
"But I knew Grant was keen to get the business up and running," he said.
Another former client Tauranga builder Andrew Etchells said he had known the Brennans since 1998/1999 when the Brennan Racing Ltd began doing some engine work on his motor racing cars.
Up to the early 2000s he had various work done on his two vehicles and understood that work was carried out by Mr Brennan, he said.
The trial continues today.
The charges
•The charges stem from allegation that the couple defrauded ACC in relation to weekly compensation payments and attendant care payments paid to them between December 1999 and September 2011.
•On April 24, 1999, Mr Brennan was assaulted by three youths while out running and sustained a head injury, and began receiving weekly ACC payments from December 1999.
•Mrs Brennan was paid attendant care payments between 2000 and 2003.
•The couple received compensation payments totalling more than $720,000. However, the amount of any alleged overpayment depends on the outcome of the trial
