When you need to exchange your money with local currency in Tbilisi, you should be alert not to be cheated.
Recently the currency exchange offices in Tbilisi have gone through some kind of transformation. Before the were buying and selling foreign currency as normal, but now they are applying a sort of commission off the transaction, as well as take steps to cheat you, especially if you are new to the rates and prices in effect in Tbilisi and Georgia. You can learn nowhere about the commission percentage, there is no sign anywhere. If you discover that your money is less than it should be, the operator just tells you that there is commission on the currency exchange transaction.
Another way of cheating is mingling with the exchange rate numbers displayed outside and inside. In a recent case the exchange rate of USD to GEL was 1 to 2.62. This was stated on the street sign. Inside there was another sign that was displaying 2.26 GEL for 1 USD. I think not everybody will notice the significant difference. They try to alure naive tourists by displaying higher than usual exchange rates, but eventually cheat them.
In order not to be cheated you'd better avoid higher than usual exchange rate signs, small exchange offices and try to find a real bank to exchange your money.