While the answer can vary according to city/county assessment guidelines, most taxes are set based on the most recent sales price in the previous year. They are then reassessed by area based on the percentage of increase or decrease in value for that particular area.

If one area of Atlanta is seeing values rise and another area is seeing a decline, the taxes should follow.

The variance in taxes ($2500 v. $900) may be that some have been held by the bank for more than a year and the value was based on the amount the lender bought it for at the courthouse steps. Others have the previous assessment of what it was paid for by the now-foreclosed owner.

Hope that helps! I would always recommend reading your assessment and challenging it for a lower rate should you feel the value of your home is not the current market value.