Brokers desperate for profit don't always play by the rules.

Literal

Profit-pursuit [to-に] desperate brokers [topic-は], necessarily rule-book [to-に] following [quotative-とは] not-limited [explanatory-のです].

利益追求に必死の (desperate for profit) and ルールブックにのっとっている (following the rulebook) — のっとる (to be in accordance with) is a formal verb. ~とは限らない (not necessarily) delivers the point. のです adds explanatory force.