Help! Critique partners bash my use of dialect

Dear Editor-on-call,
Photo credit: Sgarton from www.morguefile.com
How do we figure out where the line is between a stylized voice/dialect vs. proper grammar? I know this is a hugely "case-by-case" basis, but I often find the pieces I write with a bit of a dialect or style get corrected by critiquers for grammar, effectively changing how the character would think.

Sincerely,
Dialectable Dilemma


Dear Di,

I suspect the subtext of your question is this: "What do you do when your critiquers are so zeal...