It's even easier to trick the authors into believing you (the reviewer) is someone else.
E.g: ask the authors to cite two papers of another researcher (as was mentioned somewhere in the thread as making it easy to guess who the reviewer is), ask to compare to results of that researcher more thoroughly, use some writing style typical of that researcher country of origin, etc.
It's especially easy if you are familiar with works from the other researchers for instance because you also reviewed their work.
E.g: ask the authors to cite two papers of another researcher (as was mentioned somewhere in the thread as making it easy to guess who the reviewer is), ask to compare to results of that researcher more thoroughly, use some writing style typical of that researcher country of origin, etc.
It's especially easy if you are familiar with works from the other researchers for instance because you also reviewed their work.