My favorite thing to do if the person is being critical of me or my work, is to ask their opinion on a certain subject.

It involves them, they feel like they are being helpful, you've asked for their input and it gives them what they want... attention.

I then go and try what they suggested and next time i see them, I tell them i tried it and tell them that it either worked or it didn't work and i tell them why.

This gets them critically thinking of their own process and why it didn't work. You've listened to them, used their knowledge and politely said that it didn't work or that it did.

But, what do I know... It's not like I deal in relationships all day