Back charging the contractor arises when a certain scope of work included in the contract is either not carried out or carried out defectively. When such an event is identified, the first option for you is to get the scope rectified by the same contractor. If the contractor is unable to do so, you can retort to get it done by another agency and the cost incurred is back charged by deducting it from the contractor?s next bill. For example if a pipe supplier has supplied pipes with unbevelled ends while the purchase order called for beveled ends. You get the beveling done by another agency and back charge the cost incurred to the contractor.