Deborah Battell has published a guide, available online, for people considering offering a guarantee for someone else's debt.

It has been suggested that products such as Westpac's Springboard offer, which allow borrowers to shore up equity by securing part of the loan against a family member's property, will make guarantees more common for first-home buyers with small deposits.

Banks will be required to keep their lending to borrowers with a deposit of less than 20% to no more than 10% of their total loan books.

Battell said:  "Many people we deal with are not as informed about their banking as they need to be.  Learning from mistakes is bad enough but learning from mistakes you don’t realise you are making is much worse.  We want to help people learn without the pain."

She said the ombudsman scheme regularly saw guarantees gone wrong and some people seemed not to know enough about what they were agreeing to.

“With restrictions on low-deposit mortgages taking effect from next month, it is possible more low deposit borrowers will seek guarantors to secure funding for their home loan, and it’s crucial all concerned are fully informed about what that involves in terms of financial risk.

“More often than not, a guarantee arrangement can work well, and is a useful financial tool.  But we have found complainants with problems around guarantees are often not fully aware how being a guarantor can expose them financially."