1
The customer is always right.
Sign 'customer', then 'always', and 'right'. Make sure the 'C' handshapes move cleanly downwards to clearly establish the subject of the sentence before finishing the thought.
2
We have a new customer.
Point to yourself and others for 'we', sign 'have', 'new', and finish with the sign for 'customer'. Keep the downward motion of 'customer' crisp to emphasize the new addition.
3
How many customers came in today?
Sign 'today', 'customer', and then use the 'how many' sign. Remember to use an inquiring facial expression by furrowing your eyebrows, which is essential for asking a WH-question in ASL.