A thoughtful approach to web site quality. Some results are usually better than no results. If the user's query was bad, then the search engine should compensate with back-end logic, such as fuzzy logic that generates parallel queries based on letter substitution, word stemming, wildcarding, or some other similar approach. If the query correctly fails because no matching results exist, the interface should make that clear as well.
Relevant results are better than irrelevant results.
Quality is more important than quantity. The quality of search results functions as feedback to the user, regarding the accuracy and success of our search engine. If they see many products that have no readily apparent relevance to what they wanted, they may quit. Users shouldn't have to learn a new language to find what they want. Searches shouldn't fail because of bad data.