The main advantage of using a local tour operator is the massive price advantage that you get with it, when compared to a non-Sri Lankan travel agent back in your own country. There are many reasons for it.
The first reason is simple, by contacting a local travel agent directly, you are skipping a few parties in the loop – hence avoiding their mark-up/profits on the final price.
The second reason is that compared to the UK, Australia or most of the developed countries, overheads are lower in Sri Lanka.
For example, in the UK, you need to pay at least GBP 8.00 per hour to hire a person. Also you need to follow restricted procedures to run the business such as deposit for payment protection etc.
In Sri Lanka, however, a minimum UK salary for one week is a decent monthly salary to hire a qualified person. Also, compared to the United Kingdom or Australia requirements to run a tour operating company is very minimal in Sri Lanka.
Meanwhile, the cost of living in Sri Lanka is substantially lower and therefore, you will definitely get the price benefit when everything is considered.