Just say thier small/med sized mutts and if they want to see them personally to access then then your willing to introduce them. I mean thier not registered mixed breeds.. how would they identify em..DNA?Ha!
That way your not lieing and they are making the decision with out you sinking to deception. I understand insurance reasons also and honesty is the best policy in the long run.
you like GSD mix reminds me of dog that we adopted when I was a teenager. When we went to see them when my dad asked what breed they were the lady told him they were Royal Bo-eagle dogs. Everytime I see a mix breed even our little shih poo I will tell her she a real royal boeagle dog. I think its cute.