Gas dryer leaking gas only when it runs
It sounds like you got a real winner! I would never call him back ever!
The gas smell can be caused from several things, one common one in appliances in a garage is spiders getting in the vents where the air is mixed not enough air mixture causes incomplete burning and in some cases blocks the gas from getting to the burner.
Another problem is lint getting sucked into the mixing area of the burner and the same issues with spiders. After the gas valve the gas flow is quite small and open to the air or no pressure, the gas blowing by the vents draw air in and to the burner assembly as it exits the burner it is ignited by the pilot or has that is already lit. So I would look for blockages that is allowing gas to exit before it should, other things that could cause this a dirty burner assembly, or crack in the pipe after the gas valve or burner assembly.
I would want to identify the leak or reason there is unburned gas before something gets worse and causes a flash explosion.