If I’m understanding right, it sounds like they are doing a last-minute switch? If so, it really comes down to your cancellation policy. With no policy in place I would think you would just need to accept it gracefully and then work on a policy and post it in the salon. I require 24 hours’ notice to cancel or downgrade a service, or payment of 80% of the service price (because no supplies/tools are used) if notice is not provided. I have all clients initial my policy when I do the client intake at their first appointment. Once armed with a cancellation policy you would be able to apply it when this last-minute change occurs with their appointments. For your specific situation, I would then charge the full price of the original service if they switch, because you would still be using products and tools.
— Candice Everest is owner of Panache Nail Studio in Stanwood, Wash.