I thought it was common for a CPA to provide a checklist, which includes all forms of income.
A lot of them do.
How well the taxpayer follows the checklist, and whether the CPA cross checks the supplied data against the previous year's return, or the papers provided against the check list, are all variable.
With professional CPAs, the tradeoff is time versus quality. At Tax Aide we're all volunteer, so we have a second tax preparer double check everything on the return and with the client. We probably have an 80% to 90% accuracy rate initially, and it goes up to about 98% because of the second review. But that doubles the amount of tax preparer time *and* the client's time. Since it's free most clients don't mind the extra time, but some do.
Does the CPA have a second CPA review the return? Probably not, because it's just too costly and nobody would pay them that much. I think the most common approach is to have some one with some tax skill but less experience do the data entry and the commonsense stuff, then the CPA goes over what has been entered by the data entry person. The CPA can also handle anything weird or advanced or anything the data entry person can't figure out.
Most customers want a reasonable upfront price and probably expect perfect and thorough preparation but most wouldn't be willing to pay what it would take to ensure that up front.
As a practical matter, the CPA probably has errors and omissions insurance (or self insures for it), and it's cheaper to just pay the interest and penalties 2% of the time instead of investing twice the labor up front to reduce that error rate any further. (And not all of those 2% of taxpayers would insist on reimbursement, so it's even less than that.)
The only CPAs I trust with my weird tax questions were charging $250 an hour for their time and expertise. That was several years ago and I live in a medium cost of living city.
