It is my experience that the authorised service centres misguide customers and try to capitalise on the lack of knowledge of most customers when it comes to servicing their vehicles since the main objective of every servise advisor is maximising the billing amount.
I had taken my Alto for its third service and was told that apart from changing the engine oil, the engine also has to be flushed with flushing oil. Flushing with flushing oil costs as much as change of oil and unless the engine is very dirty (mine had barely done 4000 km) does more harm than good as a certain amount of flushing oil remains in the the engine even after draining and dilutes the engine oil when the replacement is poured in.
I observed that flushing is thrust upon any customer by Popular Motors service centre in Thiruvananthapuram whenever engine oil, brake fluid or transmission oil has to be replaced. The service manual of the car does not recommend flushing either. So beware of being flushed of your money when taking your car to be serviced!