Hi Manmohan,
Valuation rules are framed to make sure the levy. Meaning by Goods should never form part of Service Tax Levy. Service Tax is on Services provided.
Practically, in some cases it is difficult to differentiate the value of goods and service because both sale and service depends on each other. For an educational study, take an example of Gas service. Gas is provided with gas bottle. Now service tax is not on Gas bottle but on gas provided through that bottle so you should bifurcate the value of both and if you cannt pay service tax on whole amount as obviously government does not want to fall in crap of bifurcating it.
Warm Regards.