代理店(agent) is that, sellers entrust 代理店 to sell their conducts, 代理店 sell them to customers. The agreement of sale is contracted between sellers and customers and 代理店 only broker them.
販売店(distributor) is that, sellers sell their conducts to 販売店, 販売店 sell them to customers. The agreement of sale is contracted between sellers and 販売店, also between 販売店 and customers.
It may help you. http://www.english-agreement.com/article/14847232.html