Marcello: publishing a balance sheet is the best tool to keep the finance under control. If a small non-profit organization can publish a detailed balance sheet, income/expense report and cash flow report with a breakdown of program expenses then it shows the public that it is an organization that takes its mission seriously.
Every donation is an investment: the donor is betting on the organization to create social value for the whole society in the long run. It’s exactly like buying shares of a public company, investing in the hope that its management will create economic value in the long run for the investors. Would you invest in a company whose books are not visible or poorly maintained?