Co-op boards are becoming stricter about potential buyers’ financial requirements, and are tightening admissions policies, because of the financial crisis. Some buyers are finding they have to increase their down payment to 50 percent of the sale price or more, or put six months to two years of maintenance fees into an escrow account. In terms of mortgages, co-op boards prefer buyers with fixed-rate mortgages over those with adjustable-rate mortgages, and those with interest-only mortgages need not apply. Frederick Peters, president of Warburg Realty, said the boards won’t relax the rules any time soon. “A co-op board tends to see itself as a guardian of the shareholders who remain in a building, not as a facilitator of the sellers,” Peters said.