my contractor pretty straightfoward, once quoted will do accordingly unless you need adjustment on the initial quote, but if he can do, he will just do it, his way of doing ...
Hard labour (wall hacking, floor breaking etc etc) - done by Indonesians
Tiling - done by chinese guy
Painting - done by chinese guy
Wiring - done by chinese guy
AC piping (copper and piping concealed) - done by another AC specialist contractor also all chinese
So i guess labour charges are not that cheap ...
Budget more always better ......It may not due to your contractor adjust price but rather ownself