Impaired debt buyer Pioneer Credit produced strong revenue and profit growth in the six months to December but is beginning to show some of the same signs of deterioration, including a reduction in debt purchases and a fall in customer payments, that led to a fall in earnings for rival Collection House.Pioneer Credit made a net profit of A$3.3 million for the six months to December - more than double the $1.3 million net profit it reported for the previous corresponding period.Revenue was up 36.2 per cent to $21.1 million. The company outlayed $23.2 million on debt purchases in the six months to December, compared with purchases worth $26.4 million in the previous corresponding period.The book of loans operating under payment arrangements grew from $117 million in December 2014 to $150 million in December last year. Customer payments were up 22 per cent to $27.1 million on a year-on-year basis but fell between June and December last year.