Plenty of one man companies have Fortune 500 customers. Most are ran like the startup in question, as basic disaster mitigation is overhead. Don't expect the world from one guy keeping a company afloat, unless you enjoy disappointment.
From my experience you don't have fortune 500 companies as a customer as a >50person,>5mil revenue company.
You may have employees from such companies paying you via their business credit card, but will never get through real procurement without documented SLA procedures which are required to prevent a scenario exactly like this.
