Edward,
Sorry to hear about this wound you received.
I am guilty of the exact same thing that perspective customer did. I have pets that I think would never bite anyone, thank goodness, they haven't.
This "pet" owner, like me needs to be reminded that we are ultimately responsible for what our animals do.
As for having a "case".....remember the lady that burned herself with coffee? I am not suggesting you file a suit, but I would at least request that the owner of the animal cover the cost of a pair of pants, and any medical services you sought.
As for lowering you bid, if you think your price is fair - tell the customer so.
Good luck, and if you get the bid - specify that the dog must be either restrained properly or not on the property at all, while you do the work.

Tiff