wasn't和didn't的用法

有这么说的：He didn't buy the book(他当时没有买那本书.)；he wasn't buying the book.(他当时不想买那本书).又如：
1.Philip tried to get me interest in a scheme for producing a new synthetic fibre ,but I wasn't buying it.菲利普力图使我对生产新合成纤维的计划产生兴趣,但是我未上他的当.
2.When the Golden State Warriors began casting their spell on the Mavs Howard was the
only one who wasn't buying.当勇士队把魔咒撒向牛群的时候,霍华德是唯一一个不吃这套的
小牛.
如能帮上你,

第一句是对的，第二句就错了，因为buy 是实义动词不能用系动词老否定，

前一句的说法是没问题的；后一句不妥，因为buy是瞬间动词，不宜使用进行时态，而且现实中也不会这么表达。