Customizations, being highly technical and specialized, require skilled technical support that is often difficult to find and costly to retain. In addition, the final product can require a high level of skill to operate. While most CRM systems offer methods for importing constituent information, for example, these methods demand varying levels of expertise. Some systems offer graphical, step-by-step tutorial wizards, others allow Excel-file uploads, while still others demand complicated API (programming interface) access requiring advanced knowledge.
Moreover, the greater the level of customization, the higher the risk of support, update, and migration problems down the road. The less supported a feature is, the more likely it will be ignored or unsupported by developers in the future. One (more skeptical) way to think about customizations is that they are features with a user base of one.
Every service based industry provides service to their customer to retain them by taking AMC. AMC stands for Annual maintenance contract where the company charges some amount from their customer for specified product for a fixed period of time and fixed services.