On whichever online buy/sell/trade site you may be part of, how skeptical are you when a user's rating is less than 100%?

I understand things might have happened that was out of their control so I would probably draw the line around 90%. But then again I’m pretty new to the whole thing, my Swaptree rating is 0% b/c I haven’t made any trades so I would understand if someone were skeptical about me, but we all have to start out somewhere.

So any of you who may have experience with this, how comfortable are you doing business with someone who’s rating is less than 100% and would your opinion differ if were selling, as opposed to buying? And how comfortable are you doing business with someone who’s rating is 0%?