The franchise business model operated by listed home loan broker Mortgage Choice has been called into question by a joint Fairfax and ABC investigation, sending the ASX-listed broker's share price plummeting 20 per cent.Investigative journalist Adele Ferguson led the investigation and fronted the ABC's 730 Report last night in which a number of franchisees explained how the arrangement was unworkable for them.  In particular, the monthly target of writing A$1.5 million new business per month, which the ABC said was about one third higher than the industry average. Failure to meet targets will see head office take a larger share of the owners' fees.That rate sees Mortgage Choice retain a margin of 74 per cent of the revenue received on the trail commission and brokers are left with the remaining 26 per cent, according to Ferguson's Fairfax media report.Yet, the loan trail book, a Mortgage Choice franchise owner's most valuable asset, was being put at risk if the owner walked away from the business.The ABC said this forced owners to spend less time looking after existing customers in order to seek now business, along with not taking any days off, amid allegations of mortgage fraud on a par with that disclosed at other firms under the glare of the Hayne royal commission.There are an estimated 50 per cent of franchisees labelled as "low performers" who don't make their monthly targets - and who were considering a class action a few months ago. This was put on hold with the promise of a review by Mortgage Choice management, now led by a new chief executive, Susan Mitchell, who was formerly the company's long-serving chief financial officer.As a consequence of the media attention, Mortgage Choice advised on Monday, via a statement to the ASX, that it had been "consulting with its franchisees regarding a more competitive remuneration model to underpin the long-term sustainable growth of the Company and its existing franchisees, as well as attracting new, high quality businesses to the franchise network."To "partially offset the impact of any increase in the average payout rate to franchisees," Mortgage Choice said it would initiate a program to improve operating efficiencies across its business, "subject to completion of discussions with franchisees and Mortgage Choice Board approval."The company said final terms of the new remuneration model are still being finalised, aiming to introduce it "in early FY2019", which in this instance equates to "an opt?in basis across the network in August 2018"."These changes are designed to support the long term sustainable growth of Mortgage Choice, increase franchisee remuneration and attract new high?quality franchisees to our network," said Mitchell.