Moreover, users may not be able to identify which collection might hold the answer to their query. If your site provides search forms on most pages and your information architecture design includes a sectional breakdown for different topics, such as a sporting-goods web site with different sections for roller blades and bicycles, then the user may misunderstand what set of information a search query will run against. For example, a user contemplating the search form on a page about roller blades may assume that the search will only be against roller blades. If your site provides context sensitive search, users must be aware of the context, and understand that their search is contextual, to avoid confusion. Likewise, if you don't offer contextual searching, and you have distinct sections or topical areas to your site, make that clear as well.
Users have difficulty formulating queries.
Users often can't translate what they know about a product into a successful query. With clarity problems, the quality of results can't be predicted because of the uncertain validity of the search parameters. A more severe problem is when the user knows how to formulate a good query, but that query doesn't match the terminology or syntax required by the current search interface. According to a report titled Mapping Entry Vocabulary to Unfamiliar Metadata Vocabularies , The explosive increase in heterogeneity assures that the lack of familiarity required for efficient, effective searching is an increasing problem. Expert human search assistance is often needed, but a sufficient population of human expert search intermediaries is unaffordable.