Delivering after-sales services is more complex than manufacturing products. A few of the challenges faced by OEMs are:

• Deploying parts, people, and equipment at more locations than is required
  to make products.
• Support all the goods a company has sold in the past as well as those it
  currently makes.
• Each generation of products has different parts and vendors.
• Training service personnel, who are dispersed all over the world, in a
  variety of technical skills.
• Unpredictable and inconsistent marketplace because demands for repairs
  crop up unexpectedly and sporadically.