Hello Ovtolevks! I agree with Connor - I would also write "Dear Customer". Because you are using "customer" as a generic word to address (or speak to) the person that you are writing to, you would consider that to be their title which would need a capital letter. To addrees a person with "Dear Customer" is the same as writing "Dear Sir/Madam/Dr.". I hope that helps!

If "customer" is a proper noun, then it would be "Customer". This is because you are addressing them by name; names are always proper and capitalized. So in direct addresses, such as letters, I think it would be "Customer". Ex: "customer" The customer was mad. "Customer" Hi, Customer. How are you? I may be wrong, but that is how I understand it.