When a customer gets out with smiling face it means you gave him/her his required things is that true ?

Today the customer is becoming more and more aware and hence more demanding. However, the basis of customer service is empathy. If you can convey to the customer that you have understood his/her problem and will do whatever it takes to solve the problem, will make the customer happy. A smiling customer is the mission of customer service.

often this is the case,when customers are happy with the service you are provided however some customers still have the smiling face when do window shopping or do that as part of the custom

Not necessarily. However, the customer is happy that you may have given him / her an alternate solution and an answer to his / her problem