Search will return results which contain any of the terms entered.
Example: 'network marketing' (without quotes) will find pages which contain either 'network' or 'marketing'.
For an exact match, enclose search-term in "".
Example: "Network Marketing" will find only pages which contain the phrase 'Network Marketing' (without quotes).
Search isn't perfect, and doesn't find everything.
There's no fix for this, and we'd rather you knew.