My experience is that "Mom and Pop" shops are generally awash in capital to the point of forgetting to bill customers for months on end. The are "over capitlized and under leveraged" and they offset their thin margins with absurdly low fixed costs. The biggest danger to their businesses is that the proprietors might be older and decide to retire instead of toughing this out.

On the other hand my experience with slightly bigger suppliers/vendors with 5+ employees is that they run into cash flow problems all the time and do in fact seem much more vulnerable to this shock than a startup with no inventory and cash on hand.