歓心を買う[kanshinwokau] to win favour
競争売買[kyousoubaibai] auction
故買[kobai] buying stolen goods
購買[koubai] procurement
購買力[koubairyoku] buying power

思惑買い[omowakugai] speculative buying
衝動買い[shoudougai] impulsive buying
人身売買[jinshinbaibai] slave trade
人買い[hitokai] slave traffic
青田買い[aotagai] speculatively buying a rice harvest, while the fields are still green