If these people have pet insurance, or home contents insurance it will cover them for the dog biting you under most circumstances. So its not personal ie you suing them.
I wouldnt wear losing two weeks money, and not pursuing it.
What were the circs though, did you enter their garden without their knowledge, ie didnt you knock? Did they have any signs up warning of the dog?
If you are lawfully on their premises, and as the window cleaner you are, then I would think you be able to claim loss of earnings, distress, and personal injury, which would be paid out by their insurance company