I've heard of (and I've read in that popular "get paid what you are worth" book) that some firms charge a flat monthly fee for tax preparation and planning for income tax services only (no payroll, no books, no entity returns, etc).
For a monthly rate they include the income tax returns, estimated tax and withholding planning, a "checkup" to help them with their P&Ls etc, amended returns and "audit coverage" (IRS letter response, representation, etc.)
Here's an example if you scroll down the page a bit.
https://wcginc.com/fee-structure/
This interests me because I learned from my mentor do this for s corporation clients needing payroll and it has worked out very well for me. Clients love it because they know their costs and resent hourly fees. They way I've systemized these has resulted in a high hourly rate.
But I only get so many s corporation clients. I've never done it with sole props or non-business taxpayers.
Does anyone have any experience with this style of billing for income taxes for clients that are not needing any kind of writeup or payroll?