I guess the answer is simple. It's because Piggy is selfish, just like you and me and everybody else. When he negotiates with you on some computer parts, he is trying to save a few bucks; When he
helps you with some school information, he is making himself happy.
转让二手桌式计算机。SIS主板，奔腾3（733M），128M内存，20G硬盘，56K内置MODEM，内置声卡，网卡及真彩卡，音箱，17寸三星彩色显示器，WINDOWS ME及WINDOWS 2000。从商店购入未到4个月，尚有8个多月保修期（保硬件）。购入价1200元，卖出价800元。