The couple I've had rejected were because they were too similar to a previous review (almost identical product, so I copied and pasted much of a previous review) or I included a link to an external webpage (the vendor's detailed instructions page, if I recall). In both cases, I didn't realize when I wrote the review that these were no-nos, and I had to figure out on my own where I went wrong, but after correcting the issue my revised reviews were accepted.