The state agency that regulates real estate appraisers has moved to revoke a Fulton County Board of Assessors member's license, accusing him of incompetence and falsifying documents, The Atlanta Journal-Constitution has learned.

Donald Johnson is one of five assessors appointed by the county commission, charged with deciding the fair market values of homes, businesses and land lots to determine how much taxpayers get billed.

He’s also a self-employed professional appraiser working in south Fulton County. The Georgia Real Estate Appraisers Board contends some of his appraisals performed for private clients from 2005 to 2007 were so shoddy he should not be licensed to appraise residential real estate in this state.

The case against Johnson is moving forward as Fulton prepares to mail out hundreds of thousands of tax assessment notices next month telling homeowners what their properties are worth.

The state's allegations against Johnson, obtained through an open records request, cite four cases where he overvalued Atlanta quadruplexes and a townhouse, all in hotbed areas for mortgage fraud during the height of the housing bubble. The real estate board is asking a state administrative law judge to revoke Johnson's residential appraiser's license.

The judge has 30 days to make a decision after hearing testimony and arguments, but last week’s hearing didn’t wrap up and a date hasn’t been set to finish it. It’s expected to take place sometime next month.

Johnson still could serve as an assessors board member if he loses his license. He’s one of only three members who are professional appraisers.

Johnson declined to comment and referred questions to his attorney, Ted Lackland, who said his client used the best sales data available at the time and did not take part in fraud.

"He had no reason to believe that anybody was doing anything wrong," Lackland said.

Fulton Commissioner Bill Edwards, who appointed Johnson in 2006, said he will ask him to resign this week. Edwards is livid that Johnson didn't inform him of the allegations.

However, the commission can't force an assessors board member to resign over a private business matter.

Johnson is the second sitting board member to run afoul of the state. In 2010, the real estate board disciplined Rick Kenny for being "negligent" in a 2005 appraisal where he valued a duplex at $210,000, failing to disclose that it sold for $88,000 a month earlier.

The commission later asked Kenny to resign, but he declined.

Fulton’s judgment in setting values has been called into question repeatedly in recent years.

In setting 2009 and 2010 values, the assessors office erroneously used unpaid mortgages in foreclosure seizures as comparable sales. Last year, it sent overblown tax bill estimates to about 136,000 Atlanta property owners, attributed to a computer glitch and careless staff. Then in September it was revealed Fulton had appraised dozens of properties higher than what they sold for in 2010, contrary to a new state law.

Taxpayer advocates, who contend Fulton systematically overstates tax values, say the allegations show that the assessors office can't be trusted.

"This is proof," tax activist R.J. Morris said, "that the whole department is riddled with an unethical cancer, which cannot be cured, but only removed."

Three of the appraisals cited by the state were for quaduplexes -- apartment buildings converted to four single-family units -- on Hollywood Road, all of which Johnson valued at about $350,000. Appraisals must cite sale prices of nearby, similar properties. In one case, the state contends, he ignored nearby sales for $162,500 and used data provided to him by the mortgage loan originator and a closing attorney.

In 2007, Johnson and his daughter, Donna Johnson, valued a townhouse on Moreland Avenue at $240,000. In that case, rather than using sales on the same street ranging from $150,000 to $179,000, they used three properties more than a mile away, according to testimony in a hearing Wednesday.

Experts testifying struggled with the question of whether Johnson falsified documents.

"From an appraisal standpoint," appraiser Robert Hanfman testified, "I can't make any sense of it."