If anyone would seem a good credit risk, it would be Dan Martin, a custom builder in Bedford, N.H., who sold over $4 million in homes in 1989 while keeping debts down. This year has been as lucrative. Despite the good track record, Martin said he felt like a deadbeat looking for a used car loan recently when he shopped for a construction loan to build a custom home for a fully financed client. In fact, he had to go to six banks to get the loan. "Our regular bank had gone belly-up, so we had to establish ourselves anew. It was as if we were just starting business—they wanted all the personal financials, every building plan, spec, and permit —just