Any professional (including reviewer) gets or at least asks for certain dough for what they do. Why it's so shockin' after all and why 6 Moons NOT supposed to charge for reviews? If I'm a professional writer asked to write a story or an article for specific journal, magazine or newspaper, should I do that for FREE? It's only in audio-dealer's stories and fairy tales reviewers writing from listening experience. In reality, they less-likely even touch or see that equipment. All you need to have is proper audiophile vocabulary to write these articles and you don't need to be EE or designer.
Figure out. Math is simpler then science and there's no science without math.