Online Means

Do you know what happens on your website when visitors are visiting? Understanding the way searches are carried on your site is one of the most important key performance indicators (KPI: Key Performance Indicator) that you must measure very rigorously. If searches on your site are difficult to perform, your conversion rate will be negatively affected. A site with a low conversion rate generates fewer sales, thus turnover.
An internal search is not an option for your website, it is a must! You should keep in mind that an internal search is a great tool to help generate more income from your website.

So Why Should You Bother Setting up an Internal Search Engine For Your Website?
Well, I am pretty sure that your team is working very hard to generate traffic to your site. Once on your site, the vast majority of users will use your internal search engine instead of browsing the conventional way. Cyber-shoppers use internal search engines to facilitate and accelerate their researches.  If they quickly and easily find the product they are searching for, the more likely it is that they will buy on your site. So the more you put barriers between them and the product, the more likely it is that they buy from your competitor.

Analyze and Research
Reflect over this for a second. Do you know what your visitors are looking for? Are you able to analyze every phrase people searched on your site? It is not sufficient to just provide an internal search engine. You must analyze the various requests. You must understand how the searches are done and what path they follow. With that information you can make the necessary adjustments towards making your website more efficient.
The best way to begin to understand the behavior of visitors through your search engine is to analyze your log files. You'll have a preview of what users are searching and the path they go though.

Testing and Research
After observing the search queries made by users on your site, you must test the results. For example, if your users search for “product return policy", what are the results that will be displayed? Are the results are relevant to that search query? If the results do not comply with the search term, you must adjust and make some few changes on search engine.
The first results should be very relevant, because users are not inclined to explore all the results provided by your internal search engine (just like Google, Yahoo!... search engines.). So the 10^th result should be less relevant (even if it contains 100% of the information sought) than the first result.
Each key-expression (reasonable and plausible) must lead to results. For example, if someone searches for "product return policy", the information on this page should be displayed in pole position of the results returned by your search engine. Each e-commerce site should have a page with this information, so it must appear as the first result returned by the engine.
The worst thing to happen on your website would be that there is no results for a given search query. If a user enters a search query relevant to your website, he or she should and must get relevant results displayed.

Conclusion
An internal search engine is a tool used to help improve the satisfaction of internet users. If it works the way it is supposed to work, it can greatly increase your conversion rate. But If your internal search engine doesn't work well, it will lead to a frustrating experience for your website visitors, thereby causing a decline in conversion rates, a decrease in the number of successful sales which will then lead to a decrease in turnover and gross customer dissatisfaction.