A processor payout arrived net of fees, and the fee never got its own line. Revenue is short by the fee, or the fee is hiding inside a negative deposit. Either way the margin is wrong.
An owner transfer into the business account was coded as a sale. The business looks profitable. The owner looks like a customer. A lender who reads the report is reading a story the bank transfer did not tell.
A transfer between two accounts of the same business was coded as income on one side and never removed on the other. The total doubles. The match on each account still looks perfect, because each account agrees with itself.
A loan payment was posted entirely to interest, or entirely to principal, because the split was never set up. The balance sheet and the profit report cannot both be right. One of them is absorbing the whole payment.
A customer payment included a tip or a pass through amount that is not revenue. The staff or the charity is owed that money. The profit report has already spent it in the owner's imagination.
A vendor refund was coded as a sale. Income went up. The expense that was refunded stayed high. The month celebrates a fake sale and keeps a fake cost.