Why can't you add their credit card to the account? Can you also change the account details so that they own the account? Barring that, simply charge them $10+

Why can't you add their credit card to the account? Can you also change the account details so that they own the account? Barring that, simply charge them $10+n/month, where n represents the value they receive from you handling all aspects of their hosting account. You can charge their credit card on a recurring basis using e.g. Paypal, Stripe (best), another credit card gateway, or simply have them pay you up front for a year. A few hundred dollars as a lump sum is a trivial amount for a reasonable business to pay to have you manage all aspects of hosting their website for a year.