"Is he hiding income or adding fictitious deductions?"

A remodel operation means the expenses are incurred against the income fairly timely (often by benchmarks, progress, or monthly). There is always a lag in paying subcontractors. It would be nice not to pay vendors and subs until the customer pays your taxpayer client, of course.

A general contractor building "spec" (speculative) projects or flipping is not incurring expenses. Their expenditures are investing in their own inventory, not expense deductions. Their related costs are carried over as work in progress or construction in progress against the property, and that is an asset until sold. You know this as The Matching Principle, and the asset total is Cost of Goods Sold for the year it is sold and generates income.

"She uses bank feeds and assigns expenses to the entries"

So, we just reviewed not everything is P&L, some is Balance Sheet.

I like to review the differences, because expenditures and expense are not the same. The builder is looking at cash flow, but that's not your perspective. And his banking statements are not when he incurred the expenditure. The date he charged it to a credit card, not the date he paid that credit card debt, is his payment date, which can shift the year of an expense. More banking than ever is being done electronically, so the delay between activity and seeing it posted on a bank statement is less than it used to be, of course. But banking is settlement, not when the activity occurs, technically.

You mentioned net of $0, but not sales against the expenses. Sales against the expenses is a better measurement of activity.

Is he pursuing the underpayments? Is he charging interest, following with correspondence? It might be that he will have income without expenses, in that case.

Did he or that bookkeeper issue 1099-NEC timely? Is he doing lien releases? That will give you a better read on if he is a good manager for his industry or not clued in on details. You can learn a lot just from a discussion, too. He'll tell you how he charges his vehicle costs, his meals, and other potentially personal costs to the business "because I'm out there doing business." Or on the business credit card, "to make it a business expense."

And then you find they overlook legitimate activities, such as his health insurance premiums.

The IRS doesn't like seeing a loss year after year, but they have lost in a ruling that a person can just be bad at business, but still intending to operate for a profit.