One hint might be found in yearly financial reports. It depends a bit on the country if you can access those reports from non-publicly traded companies. Are the

One hint might be found in yearly financial reports. It depends a bit on the country if you can access those reports from non-publicly traded companies. Are they debt-heavy, or do they have enough free cash flow? What if all customers disappear the next day, can the business continue for an extended period of time?