Tax on Scrap Sale

As a purchaser company,,while purchasing the goods,services from outsiders , are we concerned when the party is not charging VAT or service tax or excise in it's bill relating to  supply of goods or services?

i.e. aprt from eligibilty to get cenvat/vat or service tax credit does it matter if the sullier of goods or services is registered under theses acts however is not charing any of it in his bill or otherwise he is not registered uinder these acts therefore he is not charging the same in the bill. as a purchasers of goods is it our duty to verify the same?

What is the tax impact on sale of scrap in Himachal pradesh, our manufactruing unit is located at Baddi, Himachal pradesh. ( We have scrap TMT rods from factory building construction)