Hard times are causing more homeowners to fall behind on their property taxes. But in thousands of cases, they are not responsible to their local governments, but to private companies that charge double-digit interest and thousands of dollars in service fees.

This is because in recent years struggling cities and counties have sold their delinquent tax bills to the highest bidder. It seemed a painless way to turn old debts into cash to finance schools or public services.

But housing advocates say the private companies may be exacerbating the foreclosure crisis, pushing out homeowners faster than would governments, which are increasingly concerned about neighborhoods becoming wastelands of abandoned properties.

“In the beginning, you’re getting this immediate windfall of cash,” said Anita Lopez, the auditor of Lucas County, Ohio, which sold off more than 3,000 tax liens for $14.7 million. The county includes Toledo. “But when you think about abandoned properties, foreclosed properties  the cost to the community is far more expensive than the short-term benefits.”