Many taxi drivers get commissions, the beat of course to a higher purchase price.
So do not go on an advice of taxi drivers and call them just the streets, but not the exact loading, where you want to go.
Partly get the intermediary 100%, ie the buyer (from) pays twice and much negotiating can then no longer also.
You can even take advantage of the driver's commission: if you want to take a ride, Enquire previously, whether any small shops are nearby. Give the drivers that shop and you'll better opportunities in negotiating the fare price, since the driver expects a commission by the shopkeeper.
With a little skill, In this way you can even travel for free by taxi through Thailand.