While they waited for settlement, the woman and the vendor kept in touch and the vendor allowed the woman to move some of her belongings to the house.
McConachy said cleaners and a handyman were at the house on the day of the fire getting the house ready. However, on this date, a dispute arose between the woman and the vendor over the cleanliness of the house.
The woman raised the issue and wanted the purchase price to be lowered by $10,000.
The vendor refused and it was decided they could not settle that day and an agreement was reached to delay settlement.
The vendor texted the woman at 4.43pm and 4.50pm and told her to leave the house as she didn't have possession of it and they would let the lawyers sort it.
Sometime between 4.04pm, when the handyman left the house, and 4.51pm, the Crown alleges the man and the woman returned to the house and set it on fire.
A neighbour noticed the vehicle at the property during this time and the woman's phone later showed she had been in the vicinity at 4.39pm. A security camera at a nearby house also showed the vehicle leaving the area at 4.41pm.
Just minutes after the vehicle was seen leaving, the fire was noticed and the first call to emergency services was received at 4.51pm.
At 4.52pm, the woman replied to the vendor's text messages and said: "Not now, I'm not there". The vendor texted at 5.01pm and said: "Please remove all items that you have at the address". At 5.06pm, the woman replied: "I'm in Tauranga, sorry".
The evidence from a CCTV camera showed she was not in Tauranga.
Data from her phone later showed that while the couple did go to Tauranga that afternoon, it was much later, at 5.45pm.
McConachy said the Crown would call evidence from a fire safety investigator who would say the fire was deliberately lit using an unknown ignition source.
She said it was the Crown's case that the woman and the man set fire to the house to gain a financial benefit.
McConachy said a clause in the Sale and Purchase Agreement allowed the purchase of the property to be continued less the insurance payout if damage occurred after the property became unconditional and before the settlement date.
"The property had been insured for $275,000 and therefore the insurance payout to [the vendor] was $275,000. She had already received a deposit of $17,250 and the balance that was therefore required to be paid by [the woman] was $345,000 minus the deposit, minus the insurance payout, which means she was only required to pay $52,750 for full settlement of the property."
McConachy said this effectively meant the total purchase price of the property became $70,000, which was a much-reduced value.
"A valuation obtained by the owner showed the land was valued at $155,000 to $180,000, and taking the lesser of those amounts, $155,000, the Crown says the defendants obtained a windfall of at least $85,000."
Defence lawyer Any Hill, representing the woman, said they would be calling a different fire safety expert who would say the fire was "perfectly innocent and accidental".
He said even if the jury believed the fire started suspiciously, it would be their evidence that the woman had nothing to do with it.
"She was desperate to get this deal over the line."
The man's lawyer, Scott Mills, said his client would argue he too was not involved and he was not even named in the Sale and Purchase agreement.
The trial is set down for five days.
