Basically you are tyring to evaluate the seller's performance with respect to its contractual obligations. So these are tools are techniquest for that.

Performance report is for management, Inspection and audits are compliance activities about the seller's deliverables and Procurement performance reviews , are reviews to measure how well the seller is doing with respect to contractual obligations.

For eg: When one module is completed by seller you can conduct your independent inspection to see if that complies to standards mentioned in contract. But while execution if you want to see how seller is performing you can call for a formal review meeting where seller's quality , schedule, cost etc will be evaluated against contract terms.