Lonely Planet does not condone other people stealing its intellectual property, so we should not extol the attractions of purchasing pirated or counterfeit goods in our text or feature the best places to buy such goods in a boxed text or as a top attraction. However, a general statement to the effect that a particular market or shop does sell such goods is fine as long as it is not the main focus of the review.
For many destinations, not mentioning the prevalence of counterfeit goods would be ignoring a reality that any traveller who visits a market will soon discover. (Indeed, many travellers may be visiting a destination for the express purpose of buying them.) The best approach is to find a balance between acknowledging the availability of pirated goods, without encouraging readers to purchase these goods and, without preaching, mentioning possible pitfalls and larger issues to be aware of.