I always try to stay away from neg to be honest as I am not 100% too and I myself have not seen the option to leave 0 tokens as when I want to bid I always leave a fair bit of tokens as the object is to entice them to sell. What I will say is that it is very annoying to keep receiving bids of 0 tokens from newbies or anyone even when you reject and then straight away they bid again and again 0 tokens now either they don't know how this works or they are just hoping they annoy you enough that you will sell, as regards to newbies I have always tried to help them as I was only just like them once.