Kinnick kinnick is usually made of a blend of particular traditional plants either grown by a medicine man himself or harvested elsewhere by the medicine man - or at least someone who has deeply studied the plants particular to the blend. There are commonly utilized plants and ones that aren't so commonly used, all depending on who creates the blend. As far as I know, and maybe each tribe is different with this, but it isn't forbidden to create your own blend.
I don't know if I would smoke kinnick kinnick from eBay. *If* they are being truthful about what is in the blend, I'd still research each plant that is in the blend. You never know if somebody is just tossing random plants together alongside maybe a couple of recognized traditional plants and hoping to make some money.
That's part of why I like kinnick kinnick - it is given as a gift - a symbol of deep respect and friendship - or grown/harvested by oneself. In either case, money doesn't really come into play, and the constituent plants in the blend have meanings. Smoking someone else's kinnick kinnick (like a random eBayer) to me is like smoking an extension of that person.
A better solution would be researching the plants traditionally used, and maybe other plants that may be appealing to you, and ordering them from a trustworthy source to create your own blend. The blend is traditionally kept in a red cloth, or a bag of red dyed leather. I smoke mine in ceremonies, during important talks, or just when I want to commune with nature or pray. My personal kinnick kinnick blend contains many plants that I have harvested by hand from my travels over the USA or have grown myself in my garden. I also use various tobacco blends as well, mixed in.