May mortgage sales at Australian Finance Group have slumped in comparison to previous years - traditionally a high point in the buying cycle before winter.The $2.2 billion value of May 2008 AFG loans has fallen a quarter - or $875 million on the corresponding month a year before, and $371 million less than May 2006.The May national mortgage average value was $334,000, the highest monthly average in the four years of the index - indicating that the broker group is sourcing loans from higher net worth property purchasers in the current climate.AFG said demand for introductory loans (with discounted rates in the first six or 12 months) was much higher in May (at 12.8 per cent of new business) than in the four years it has compiled this data for external publication.Demand for fixed rate loans fell to 13.7 per cent of new business, down a third on April and almost half on March.