1) (modal) want
From Wiktionary: https://en.wiktionary.org/wiki/mu%E1%BB%91n
How come it isn't "có muốn" here?
"Buy" "mua" sounds to me like it is high rising, when it should be a level tone.
No it's definitely not a sắc tone. Even with tonal languages, there is often variation from speaker to speaker.