Bad quality goods may be found in Warehouse so quality ensure by QC department is mandatory before receiving goods in Warehouse - is it true?

Yes, but the QC must clarify the required specifications and conditions of the material in question and subject to the test by the end user or testing department

Yes, the best is sampling method, but first it shall be made clear to the vendor of your standereds, prior to adopting it.

Yes but not for all parts ..Its necessary for special case. 

Also proper training on product should be given to Wh team since every bosy in the organisation is responsible for quality control.