Not everybody can handle work in progress critique. Here are few thoughts that might help:
If you ask for a critique you should have a clear idea of what you did so far, what is missing/wrong/not jet how you want it and what is good/great and can stay this way. Then the critique will not harm your process because you chose a good timing (after your own analysis) to get some fresh thoughts on you work.
It is a good idea to ask for specific points: Do you think this colors fits in the painting? This will help you more because the answer won’t be generic and the question will specify your own thoughts.
It is important to think about who you ask. Has the person more or less knowledge, skill, experience than you? (Here you should think about the value of posting work in progress shots on social media.)
If you did not ask for a critique and you don’t want to have it then say it clearly, but friendly. Most people will understand immediately.