Insects are extremely resilient and harbor in locations much difficult to an untrained eye. An Official Pest Prevention specialist is aware of such locations and can make expert recommendations on what is necessary to eradicate these pests. A licensed pest control company also has products that are much more effective than those sold over the counter at "do your own pest control" stores which helps to deliver precision pest prevention. Also, online pest control courses found online can vary from state to state making it difficult for a homeowner to achieve desired results. Local pest control companies will have direct experience with the pests you are seeing and have much more experience ridding you of these pests.