From Wikitravel

Sometimes a restaurant, bar, hotel, or other attraction has such grave defects that it's just not worth going to. If this is the case, it's best to just leave it out of the destination guide for the place it's in. There's no reason to clutter up a guide with lists of places travellers shouldn't go.

The exception to this rule, however, is when travellers may be led to the attraction by other information sources. For example:

• The attraction is prominently featured in other guidebooks.
• The attraction is widely advertised.
• The attraction is prominently located — across from the train station, right in the middle of town.

In these cases, write an attraction listing as for places that are recommended, but in the description note that the place isn't worth going to and explain why it should be avoided.

If a destination has only a few reviews (or a few accommodation options), and some are negative, do not delete them — some information is better than none.