Hair Salon: How to collect final payment when services are completed-Deposit was taken when client made appointment

We in the testing stages before we go live.  We are collecting a deposit when booking online and can't figure out the check out process when a client is at the salon and services have been completed.  Also, is there a way to add to that original appointment if the client decided to have additional services?  Also, how can we book a clients next appointment with the receptionist and ALSO collect the deposit?  

Thank you!