Is it legal to buy a used car just before filing CH 7 in Georgia?

You could be commiting fraud, not only in Georgia, but in any of the other states or possesions. It is not illegal. You will, if the car is not covered by the vehicle exemption have to forfeit the car to the BK trustee. If the car was bought out of necessity, such as it was needed for you to get to your job, it will probably not affect your BK filing. On the other hand, if you just "wanted to buy a car", you could have a problem getting the bankrupcy discharged.