Ahead of its first round of hearings next month, the Royal Commission into Misconduct in the Banking Superannuation and Financial Services Industry has published its second background paper, this time on the mortgage broking industry, a key distribution channel for residential mortgage financing in Australia.One of the themes running through the paper is how little publicly available information on crucial aspects of this sector is available, given mortgage brokers were involved in settling 55.7 per cent of all residential home loans in the September quarter 2017, and banks still finance the majority of the loans originated through mortgage brokers.Even detailed publicly available information on changes in the number of mortgage brokers and mortgage aggregators over time is limited, with the paper relying on the MFAA's figure of 16,009 mortgage brokers as at 31 March 2017.  Many of these - perhaps the majority of active brokers - work in small offices of one or two brokers.However, there is no public information on the total number of mortgage aggregators owned by ADI lenders, although the Productivity Commission has estimated the combined market share of these aggregators was just under 70 per cent as at December 2015.Nor is there more than "limited public information on the characteristics of loans arranged through the mortgage broking channel", making it difficult to analyse the comparative credit quality of mortgage broker originated loans.And when it comes to payment to mortgage brokers and mortgage aggregators, generally they do not charge borrowers directly for their services, relying instead on commissions. The two main types of commissions are upfront and trail commissions.  "Again, there is only limited public information on the value of commissions paid to mortgage aggregators and mortgage brokers by lenders," the Royal Commission paper said."The Productivity Commission has observed that information on commissions paid by lenders over time appears 'to be a black box for this industry'."In its January 2018 draft report, the Productivity Commission did not present any findings based on unpublished industry data, as it did for upfront commissions, although ASIC reviewed some payments in 2015.