for those that master the intricacies of wholesaling in Europe stand to reap considerable gains.这句话 中,that master the intricacies of wholesaling in Europe 是一个定语从句,修饰those.主句是 those （主语） stand to reap （谓语）considerable gains（宾语）.stand to reap 是（谓语）,自然不能用standing 了.