Handling a Key Account is a significant investment in resources, and the company should consider the expected return on this investment prior to this decision. It's not about "being nice" to a loyal customer, it is all about building more value for a customer who is ready to invest more into your company.
A company should consider "promoting" a customer to a Key Account status under the following conditions:
the customer is contributing a significant revenue to the company, and the company is ready to invest into dedicated resources looking after this customer
the company has a portfolio of products/services that could be leveraged with a closer relationship management and the customer has potential for even more important spendings
In the end of the day, it must be a win-win decision, nothing else
Over a period if you are achieving major chunk of your revenue target from an account then it's time to start looking at it as an account. Continue this and then keep making assessment periodically.
No organisation can be considered as a major account for life long without being assessed its potential from time to time.
