I'm near Knoxville and use the Co-op in Greenback. The first couple of times I went there, they told me the same thing and "grilled" (my word) me on "is it for farm 'food production' uses"
Though we are not raising crops on the "farm" where I live, I told them yes anyway, because indeed it is for offroad use which was their primary concern.
I also told them another time, "dunno... you tell me, I'm using it in my backhoe" The guy says.. "ahh, ok, THAT is construction fuel" (his implication seemed to be a different rate of tax).
Upshot, I've always ended up with the red 'no tax' fuel and now that I've been there several times, they don't even ask.