Enterprise software implementations require software vendors. You will be spending a considerable amount on Professional services with these vendors. So, before engaging them, make sure they are trustworthy.
You may also need a client-side Project Manager (PM). The client-side PM role is to work in collaboration with vendors PMs. Both PMs must collaborate to deliver the successful project within scope, quality, budget, and time constraints.
It is pretty common to see client PMs justifying their existence through fault-finding. Their focus is to question vendor invoices and timesheets. Thus, you will see them taking much pride in nit-picking vendor work.

The client PMs have a critical role to play. Their focus must be on managing all tasks that are client responsibility. For example, Analysis, Data, Testing, Training, and Change Management, to name a few. In addition, they must work constructively with all stakeholders to deliver the expected outcome of the business.
Understand the ‘Manage Software Vendors’ dynamic
In Summary, as a Project Sponsor, make sure you engage trustworthy vendors. The client PM role is critical for project success. Therefore, client PM must work in collaboration with all stakeholders (including vendors). If the client PM has to manage software vendors. In other words, police the vendor’s work, then you are not utilising your resources effectively.
Take some time to reflect on this dynamic. Why do you need to pay someone (client PM) to manage someone else who is paid to do the agreed work (vendor)?