a secret of the third tone
Third + Third = Second + Third: nǐ hǎo should sound like níhǎo.
Third + Second = Half a Third Tone + Second.
The 3rd tone can be produced in three different ways:
first half of a "3rd tone",
second half of a "3rd tone",
full 3rd tone
Duration is key, considering that the 3rd tone is the longest tone, and in situations where duration is obligatorily short (eg. fast speech) you will lose the full features of the tone contour and be left with what I imagine you are identifying as a "low level tone".