I detest these issues, but they can arise from time to time. It's even worse when a client has turned sour for some reason and are just being ridiculously demanding and unrealistic.
The first thing I realize is that the client is upset for some reason, which means they are of a mindset to just get "everything" without any considerations towards me. To that end, I know they see their requests as valid, mostly due to anger, even if they aren't valid requests. So, I try and treat them as I would any client asking for more than what they have a right to. I try my level best to not be hotheaded or outright argumentative and leave emotion out of conversations as much as possible (which is more easily typed than done at times.)
My first course of action is to refer to any contract. Repeat or cite clauses there if they pertain to any demand. My contract specifically states what a client does and does not receive for payment.
In the scenario posed in the question my response would be simple:
"Referring to our contract, only final files and completed works will be delivered. Preliminary sketches, rough ideas, and preliminary comprehensives are not part of our agreement and will not be supplied. Such items remain [my intellectual property/the intellectual property of my company, XXXXXXXX]."
Now, realistically, not every project may have a contract. Yes I know bad practice, but it is real-world in many instances. So, without a contract any client is not entitled to anything you do not wish to provide and have not agreed to provide.
US copyright law specifically states the artist retains the rights to everything other than in 9 instances, 10 if you count employment or work-for-hire situations. If the work is not part of a test, a video, a compilation, etc you still own the rights to everything. [ More info here.]
So, given this, one must look at what you've agreed to in writing.
"I said I'd like to quit and am willing to give them all their final files"
So you've agreed to provide final files. If the client is requesting more than final files, you need to define what "final files" means....
My typical response in similar situations is:
"Preliminary files remain the property of xxxxxx (my company). I'm willing to provide final [pdf/png/jpg/ai] files for XXXXX and XXXX for the price we agreed upon. However, any preliminary sketches, working roughs, or comprehensive designs created in the exploration of a final design solution will not be provided without additional fees to be paid prior to delivery."
This will, in all likelihood, anger the client more, so be prepared. You'll get the "we paid for the design, we have a right to the files." and all those misguided arguments much of the time.
"This is standard practice. It is customary for preliminary files to not be included with deliverables without additional compensation. This is inline with practices suggested by the American Institute for Graphic Artists (AIGA). You can read more in this article: http://aigasf.org/legalities-33-do-you-have-to-give-your-freelance-client-your-digital-files/"
In the end, it's all a negotiation....
How concerned are you with having an unhappy clients?
Will you be losing any word-of-mouth business do to this?
Remember one unhappy client can spread negativity like a wildfire.
So I tend to ask myself....
- Will I otherwise profit from the files they are requesting?
- Can I reuse these files in some other future project?
- Can these files be repurposed by them for some other use beyond the intended design?
If the answer to these is "no" then I'll provide more than simple final files. If there is no value in my retaining the files, I may as well use them to try and placate the client, at least partially.
I may provide a couple earlier comps that they may find useful, but would be of no future use for me. I tend to "give a little" here if the files have no other value for me. The goal is for the client perceive me as being more amenable. It makes it appear as though I'm more responsive and willing to compromise. Truth is I'm just trying to avoid any unnecessary bad word of mouth. If the client feels as though you worked with them a bit and "got their way", they are less likely to seek out opportunities to bad mouth me.
Note that I don't provide anything which may take a "couple hours" to clean up and prepare for delivery. I provide files which are easily prepared and don't require any effort to deliver. I won't put in hours of work to deliver anything of a preliminary nature, especially to a client I'll probably never see again. But if I can merely open a file and export/re-save it... I may provide that file.
If the answer to 1, 2 or 3 is "yes" then I stand firm and don't provide anything without additional compensation.