Like most of you, there are 3 things that immediately turn me off to a seller:
1. The item is listed as rare or scarce
2. Has not been tested so I don't know if it runs
3. Item sold as is, seller does not consider returns.
It would appear that you haven't had a lot of experience selling, at least on Ebay.
With respect to no. 2, if it is a new item, and you run it to test it, it isn't new any more and can't be sold as such. This can cost the seller a lot of money. Usually, buyers prefer an item that is new, and it generally carries a higher value. Obviously collectors want new, unused items as well. If I have a new, unrun item, I never test run the item before listing it.
With respect to no. 3, many sellers put that statement in to hopefully discourage buyers who are just "kicking tires," and will return an item for almost no reason, if they decide for any reason they now no longer want it, or they now need the money back they spent, and other frivoulous reasons, or if they damage the item after receiving it. If fact, with Ebay's policies, the buyers can almost always return an item anyway regardless of whether it's listed "sold as is."
I've had a number of instances where buyers have returned items because after they received it, they dropped it or otherwise broke it, or damaged it in some way. Right now I have a relatively expensive JLC UP Challenger that the buyer returned, which was new when I sold it, and was returned with bent parts on both the engine and the tender. Every ladder on the tender is severely bent, several completely bent in half and gnarled. The buyer got a full refund, and I'm left with an engine that has lost many hundreds of dollars of value, in addition to losing another $40 in return shipping cost I was tagged with.
I get a little defensive sometimes as a seller, because over the years I have been ripped off by buyers more times than I care to think of.