Hotel staff, tour desk staff & tour guides in Thailand make most of their money from commission and under-the-table payments. It is always possible to find a few honest people, but it should be understood that many people are often paid little salary & the tourism industry is such that many unlicensed people can get commission just like travel agents of up to 75% of the selling price.
Everyone should also understand that a travel agent or tour desks have to make a certain commission to pay for their services, like any middleman around the world for any business. The client should always compare, read, ask for information from the agent about whether the trip they buy is worth the price they pay. If you are paying a high price and get satisfaction, then there are no reasons why the agent or tour desk should not get commission for recommending a good tour, but if the tour is of very low quality and you aren’t satisfied then you should complain and you are probably not going to be happy knowing the agent got commission.