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Let’s play “Who’s the A$$hole?”

My firm provides an outsourced accounting department to business clients. We keep their books, run their payroll, and prepare their financial statements in accordance with GAAP. However, we don't prepare their income tax returns. For our services, we charge a flat monthly fee. 
After year-end, we send each client's annual financial statements, trial balance, and general ledger to the various firms that prepare the clients' tax returns. We don't do anything to these files except export them from the system and transfer them to the tax preparers. 
Around Feb. 1 this year, I got the following call from one of the tax preparers (TP):
TP: These files you sent over for XYZ Partnership, LLC are all wrong. You gave me book financial statements and a dump from the GL. I need cash basis financial statements, and I need the health benefits expenses for each business owner broken out separately. Oh, and I need you to book half the depreciation on these fixed asset additions in the current year under Section 179. Why did you straight-line them?
Me: I can see why you would need those things to prepare the tax return. However, that's not within the scope of our engagement with the client. Converting book financials to tax financials are part of preparing the tax return. You should have everything you need to do that in the files we sent you.
TP: Look. I don't have time to do your job for you. When I receive the client's financials, I need them to be ready to enter into the return.
Me: Like I explained, that's not what the client hired us to do. Did you include converting the financials in your engagement agreement with the client?
TP: I'm not going to discuss the engagement agreement with you.
Me: We work under a fixed-fee arrangement, so it's not as if doing the conversion would bring us more billable hours. If you want, we can both talk with the client and see about getting a portion of your fee re-allocated to us.
TP: Ha ha! That's a good one.
Me: I'm not kidding. Otherwise, you should talk with the client about increasing your fee if you think you're being asked to do something out of scope.
TP: I could say the same to you!
Me: The client hasn't asked us to do anything out of scope. You have.
TP: Thanks, asshole. [Hangs up.]
Who's the asshole?