how to stop the mouthing

My dog Fiona mouthes us to say hello. we usually will stop trying to pet her until she turn around and let us scratch her back, and stays still for more than a second. She has diminished this behavior at home, since we got her. She is a two yr old rescue, and is DEAF. No idea what her behavioral baggage is. The problem is that she sometimes wants to mouth strangers that want to pet her. Ad does it in a play way, you know quick, sort of snapping.
It is not aggression, it is just play, but I would love for it to stop. Its really bad doggie manners.

I might start giving treats to all strangers that want to pet her.

Sorry I don't have any experience of living with a deaf dog, hope the links below help:

http://staffy-bull-terrier.com/living_with_a_deaf_stafford

http://www.deafdogs.org/training/signs.php#signs

If she mouths you, try putting hot sauce on your hand, might deter her from mouthing you then she might not stangers? This doesnt work on every dog though my 13 year old springer spaniel actually likes hot sauce so didnt stop him at all haha