On average, listings lease in the $20's per square foot per year. The Marietta submarket is going through a an increase in rates. In the last 3 months, the median rate rose $10 per sqft per year. That's a 68% rise in rent.
Compared to the rest of the Metro Atlanta market, the Marietta region has lower rates, so you should have no trouble finding a great deal in this undervalued region.
In the last 90 days, 40 listings have come on the market, which means new availabilities most likley are leasing quickly. You'll want to be prepared to make an offer immediately. There aren't many listings below 2,000 square feet posted, so finding a space for a small business might be tough.
Even though the median size is 2,840 sqft, there are still 0 leases below 2,000 sqft. Most properties in this region are around 2 stories. Most buildings in this area were built in 1986 and are Class B.