The company I work for sells products from hundreds of vendors. Some of these vendors do not want us to sell their products on our website (only in the store), because they do not want us to rank if people search for their products. What we would like to do is offer the products on our website, but not allow SEs to index the product pages, so that we do not rank.
The problem comes on category listing pages, where we would list both normal products and those that we cannot rank on. We essentially have 2 courses of action: 1) allow the products to be listed, and hope that because there are very few, and they are spread out over several pages, we won't rank very well for them, or 2) determine if the visitor is a bot, and not display the restricted products to them. There is a similar concern on a page where we list all of the brand names we offer.
I think in general, black hat techniques to cloak involve showing more or different information to SE's, where as we would be offering them less information. Reading through Google's guidelines, the rule of thumb seems to be "is this helpful for the user, or deceptive?" If this is the only litmus test, I don't see a problem, but I would like to get advice from anyone else who has done something similar, or considered it.