My English is pretty advanced, yet I still make mistakes (not many, but some).
I am constantly talking to native speakers and always tell them to correct my mistakes.
My problem is that in most cases they just won't do that! The keep telling me that my English is so advanced that they always understand what I am up to and I keep telling them that I still feel embarrassed when I find out afterwards that I made a mistake.
Obviously this is some combination of misconceived politeness and laziness.
How can you encourage persons to correct the mistakes you make?