If there is a substantial increase in bad debts, what might this mean?

In the case of lending money (for a vehicle or a mortgage for example), this may be an indication of irresponsible lending practices. If there is a substantial increase in bad debts, it means that less creditworthy borrowers (borrowers who are less capable or likely to repay) are obtaining credit too easily.

In the case of bad accounts receivable for a company, there are similar implications, but it also could mean that the inventory that a company is selling is not being sold quickly enough by the retailer. One example could be ToysRUs having overdue accounts due to its partnered toy makers, such as Hasbro. It could be a sign that the demand for the product is not sufficiently high to sell the full amount of purchased inventory, at least when being sold through that retailer.