Since the end of last year, home equity lines of credit have been hailed as salvation for lenders facing an increasingly competitive market with lower origination volume. But while some lenders have been successful in HELOCs, many have difficulty turning a profit with the low-balance, paperwork-intensive product. Some experts say the trick to HELOC lending is the documentation. Terry King, group chairman at MRG Document Technologies, said that what trips up lenders the most