Do book review copies sometimes end up for sale on Amazon?

Good firms like ours take precautions to discourage review copies from being resold on Amazon. First, we carefully select where we send review copies. Second, we stamp each book with Review Only; Not for Sale to discourage reselling. However, some media contacts, book reviewers as well as readers who have purchased a book do resell online. It happens to most books, especially ones written by famous authors.