In recent years, the motives for mergers have increasingly changed from cost-driven mergers to market-driven mergers, which intend to improve the market position, to enlarge the product portfolio or to get access to new markets. Therefore, integrating the marketing and sales (M&S) area plays a significant role to achieve the merger goals. M&S is the only business area with direct interface to customers. As a result, post-merger integration (PMI) activities in M&S have direct impact on customer relationships. However, various empirical studies reveal that companies have real problems to realise the expected benefits. To find an answer to this phenomenon, the author investigates possible reasons and identifies the neglect of the PMI phase and the missing expertise how to merge M&S as the major bottlenecks.