Are they afraid that self-published authors will stop sending free review copies? Well, in that case, so what? The vast majority of these publications can't be unloaded for cash at a used bookstore, so you lose nothing if people stop sending them. Some of the top reviewers are doing just fine padding their collection of reviews with fluff pieces on items major publishers will notice and care about. There's no need to do so much for one dude in Kentucky who thinks he is so skilled in Spanish just because he got a B.A. in it.
When I tried to post my 2-star review, it did not appear on the page, and is presumably being held for evaluation. For what it's worth, here it is:
As I am an Amazon Top Reviewer, Brandon Simpson sent me a copy of his book DEMYSTIFING SPANISH GRAMMAR. Unlike some others here, I'm going to give the book the evaluation it really deserves, because learning a foreign language is a serious business, and people deserve the best tools. Simpson received a B.A. in Spanish and has worked as a Spanish tutor. He noticed that his pupils had especial trouble with a handful of Spanish grammatical concepts: 1) the use of accents, 2) the difference between "ser" and "estar", 3) the difference between "para" and "por", 3) the distinction between the imperfect and the preterite, and 4) the use of the subjunctive. He decided to compile helps on precisely these issues.
The result is all but unusable. When dealing with foggy areas, like the difference between the preterite and imperfect of "estar", Simpson asked random Spanish speakers instead of citing trustworthy studies prepared by trained linguists. There's little coverage of the considerable differences between Latin American and Spanish usages, nor literary Spanish (which form the small town American student will probably encounter more than the spoken language). The book appears to have had no professional editing and is amateur in all respects. On the back cover we find "This Book Will Demystify... the Dreaded Spanish Subjunctive!!!" Using exclamation points so abundantly doesn't inspire confidence. Inside, misspellings and lack of punctuation abound. Typesetting was done in a word processor, Microsoft Word, instead of a suitable typesetting engine and the result is hard on the eyes.
I'll give the book two stars because the grammatical paradigms within aren't wrong. However, the student of Spanish would do better to get the [[ASIN:0007224206 Collins Gem Spanish Grammar]], a nice little pocket-sized reference of all aspects of the language, including a number of completely conjugated verbs, still widely available available on the used market.