1 - Try to take photo of car Number Eg. EE-3190, from back. If you are not alone it can easily be done before entering to taxi. If you are alone you should find ID card on dashboard and take capture or even you didn't find it try to take the driver photo and car silently.
2 - Try to show your map or GPS to drivers that you are knowing the way they should go.
3 - Do not let him to take another passenger on the driving way .
These three things should be done when you take taxi in Yangon.