Criticism in need of clarification

A critic often conveys what underlies her criticism, but imprecisely, leaving it unclear to the arguer what argumentative strategy to adopt. I elaborate on the opponent's “burden of criticism” by using argumentation schemes. For example, the critic may challenge a thesis by saying “Why? Says who?,” without conveying whether she could be convinced with an argument from expert opinion, or from position to know, or from popularity. What are fair dialogue rules for dealing with unspecific criticism