Photoshop :: Professional Ethics With Clients

I’d like to get some feedback on the following:

I have been working with a client who has recently requested an un-flattened version of the work I have been doing for them. They have been impressed, and at times inquisitive with “How’d you do that?”.

I am contemplating responding in a diplomatic way that I must decline. A version with all layers available will show many of my methods (and tricks) I have developed over the years, and I should not have to divulge them to a client.