Its often said that you should be weary opf buying carbon (carboin filters) from Ebay as you cannot tell spent , used carbon from fresh. Like alot things you get what you pay for, I took the approach of reasearching the product I wanted and then scoured the internet up and down for the cheapest prices. Then you here people saying you need supplemental odor protection and I wonder, what brand -good,cheap,unknown, the area it is scrubbing, how it is installled, ect.
I went with products that have solid reviews and warranties. 6in Vortex fan, comes with 10 year warranty. 6x24 (there is a smaller think it is 6x12 but it is not rated for the 6in h.o. vortex fan) carbon filter by Phresh. They use crushed carbon vs. pellet carbon which mades for less leaks past the material and more surface area to scrub the particles from the air.
Needless to say I can stand right at the exhaust and stick my nose in it and not smell anything
On a side note: High humidity levels will kill the life span of carbon.