Scotty,
My
completely-not-official answer:
Do you want space reserved for you? Are you there to have a little fun while you sell or sell a little while you have fun?
I see you're not trying to abuse the "I'm just here selling a few things while I'm flying" swap-shop nitch -- I don't know of an event that at least a little of that doesn't happen -- and all but true "swap-meets" allow this for no more than the landing fee.
. . . but most bigger vendors have somewhat prime space, pre-reserved and paid for. If you're just taking the first pit spot available on the flightline and among the things you're flying you're selling a few things, that's totally within the spirit of they guy who had an old plane he didn't want anymore so he slapped a "for sale cheap" sticker on it.
Now if you're stringing up a banner, hanging out a big sign -- even if you aren't selling anything, you're selling your brand -- then, you're a vendor in sprit.
For instance, at SEFF last week, Atlanta Hobbies had a reserved spot where they rolled in on Wednesday, set up some eazy-ups and tables and pulled out a selection of custom and RTF high end AP multirotors. This is one of their bread-and-butter markets, and I wouldn't be surprised if they had >$100k worth of gear out on their tables. IIRC, one of the employees sold a DLG on-the-side from the booth, but other than a few inspire parts they may have left in the woods, I think they left with every multirotor they brought.
Vendor? Absolutely. They got a reserved space and rigorously sold their brand.
Next door was my little eazy-up. Over the weekend I sold a quad I'd built on spec and Josh sold a handful of gliders and an airframe or two. We *probably* made more money at the event than our neighbor!
Vendor? Not hardly! No ads beyond the FT shirts (Best answer: "Hey are you with Flite Test?" "Nope, but we're family"), no reserved space, and we were there to fly and chat. The stuff in the tent and what we did with it proved that true.
If you're there to have fun while selling odds-and-ends and a few frames, but not trying to build up sales and brand recognition, I'm not sure I see the difference between you and the swap-shop pilot.
That being said . . . I am by no means official in that answer -- FT can completely disagree with my viewpoint, and since it's their event, whatever they decide is right by definition. I'm just trying to better define the spirit on both sides of that line