Business information avilable on internet is accessed by people or not?

This question is very basic interim if sales person in giving the presentation on online marketing or somebody asking do I need to advertise on online. Who will search for my product & services?

Everybody is more interested into advertising on internet/online if their prospective customer is online.

Every type of business in specific segment has products or services to offer and if you closely think and pen down you come to know what if you have to put yourself in shoes of customer than what they might be looking for like for example : -
If you are living in Delhi, India. You want to get root cannel from the dentist than you might be searching for dentist in Delhi. Now we have a simple business keyword “dentist in Delhi” which most of the customers living in Delhi might be looking for the same keywords. There are allot many keywords your customers might be search on various search engines.