Break it down for them and let them know. Part cost is researching what part is needed, ordering the parts from a trusted source (No Amazon knockoff), picking up the part, warrantying the part, and having an experienced person to install it. They are paying for a service and part of that service is knowing what part went wrong when it breaks. If it was so easy and cheap then they should have done it themselves. They are not paying just for the time it takes to fix an appliance they are paying for your years of knowledge of knowing how to fix it.

We usually do a dinner, $200 gift card (Also do a $100 for Thanksgiving), and jacket/coat.

I had a customer that was doing about $1.2-$1.5m a year with and average GM% of 26% consistently for 8-10 years. The sad story of the owner gets a divorce, gets into drugs, starts partying, and starts to ignore the business and it folds. All the customers that replaced the folded business were all out of state buying in their home states. I have recovered some of the lost sales in other customers but trying to find an extra $350k in GM a year has been rough.