(That's me trying to be positive and thankful.)
Even though we had them professionally cleaned before we moved in, on a hot day they still smell a little bit like the previous owners pets who liked to pee on them. And since we can't afford to replace them just yet, every few months or so I like to give them a little freshening up.
I've used retail carpet powders and febreeze and aside from the cost, these things work just O.K.
But the cheapest and best thing I've found so far is a recipe on the internet for Homemade Carpet Freshener. I've tweaked it a little bit and it goes something like this...
Homemade Carpet Fresh
Process 2 cups of baking soda, 2 cups lavender buds, and 2 cups of rosemary in a food processor or blender. Store in an airtight container. When ready to use, sprinkle on carpets and let set for an hour. Then vacuum up.
This would probably work well with another of your favorite herbal scents also. Don't be afraid to experiment.