Hillary Rodham Clinton’s cash-strapped presidential campaign has been putting off paying hundreds of bills for months — freeing up cash for critical media buys but also earning the campaign a reputation as something of a deadbeat in some small-business circles. A pair of Ohio companies owed more than $25,000 by Clinton for staging events for her campaign are warning others in the tight-knit event production community — and anyone else who will listen — to get their cash upfront when doing business with her. Her campaign, say representatives of the two companies, has stopped returning phone calls and e-mails seeking payment of outstanding invoices. One even got no response from a certified letter.