Chartered quantity surveyor Alfred Hill claimed previous costings made by prosecution witness Derek Bate for work carried out at Annie Lennard Primary were not always accurate.
It comes after prosecutors alleged defendant Joseph Hollingsworth was involved in a conspiracy which saw estimates for work at the Smethwick school “inflated”, with invoices created for work which was not carried out.
Giving evidence on Friday, Mr Hill said he “disagreed” with chartered surveyor Mr Bate on the pricing of various work, including materials used and labour costs.
He added: “I don’t agree with his prices, they are totally inadequate.”
Mr Hill, who was called as a defence expert witness, visited the school on March 19 to view work which Joseph Hollingsworth Ltd allegedly carried out between 2009 and 2010.
The witness told jurors there was “no mention” of certain work in a report from Mr Bate, including work to pull down a cupboard in the school.
Mr Bate also did not include an approximate £200 for a site survey prior to Joseph’s Hollingsworth's company fitting a new bespoke fire door at the school, Mr Hill said.
He added: “Somebody has had to do the site survey so that the door can be made.
“Without doing a site survey, you don’t know how big the door is that’s going to be made, so you can’t get the door made.
“Somebody has to go to the site. It’s costing that is incurred and it’s justified to be reimbursed.”
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The witness went on to say it was “just not possible” to carry out work to fit the new fire door based on Mr Bate’s £360 estimate or within his four-hour time frame.
Explaining his work, he told Wolverhampton Crown Court: “I walked round the whole of the school with Joseph Hollingsworth and the work that had been carried out was pointed out to me.
“I then made various notes and sketches which gave me sufficient information which when I was back in the office, I could properly measure the work and put a price on it.”
During the trial, jurors heard Mr Bate checked invoices against work actually carried out, examining a total of 168 purchase orders.
He claimed there were disparities in some costings - including an £11,850 invoice to the school for fitting kitchen windows, roof lights and aluminium doors, compared to the surveyor’s estimate of £4,350.
Prosecutors allege headteacher Michelle Hollingsworth, 55, and secretary Deborah Jones, 57, systematically syphoned cash between 2010 and 2015 by using the school’s cheques and fake purchase orders.
Joseph Hollingsworth, 58, of Hatherton Park, Cannock, denies assisting his wife to purchase, collect and transport goods which had been obtained through fraud, and attempting to pervert the course of justice.
Jones, of Barrs Road, Cradley Heath, admits conspiring with the headteacher to defraud the school and Sandwell Council but denies all other charges.
Michelle Hollingsworth, of Hatherton Park, Cannock, denies conspiring with Jones or anybody else to defraud and also denies attempting to pervert the course of justice.
The trial continues.