can anybody assist me with this:

i'd a potential buyer who haven't 100% confirm that he want to buy from me. before i get the chance to settle with him, he already posting his dissatisfaction comment on other seller thread! this is not only will ruin my name & business but also, it'd affected other ppl business thread as well.

can we report this sort of 'person' anywhere? can anyone suggest what action should i take to resolve this?

thanks.