这句话去掉从句就是 Salespeople conclude and fail to see the benefit!
who 引导定语从句 指带 salespeople ,salespeople who believe that!that是believe的宾语从句!
conclude that ,that引导conclude的宾语从句!
benefit that,that引导 benefit的同位语从句
所以这句翻译为：”那些认为给出来的借口是和合法理由“的销售人员认为”下架胜于买卖
,而且他们看不到厂品销售服务将会带来的效益!（感觉翻译怪怪的,应该是有上下文的）