But, Lisa, just because other companies are worse does not mean that this is okay. Why do we base whether somjething is acceptable based on the worst case scenario?
This is MCP's issue and they should not put the onus on the shopper. The shopper has fulfilled the contract for the shop by completing the shop and should get paid in full. If MCP (or any other MSC) would like additional work done, they are free to make a new contract with the shopper for those services.
It is total BS for the shopper to take on the technical issues if the MSC's. We already take on a lot of risk. If I have technical issues which result in me having to redo work, I just do it. It is my responsibility and I accept that freely, albeit not necessarily cheerfully. I don't contact the MSC and ask them to kick down a few more bucks because I had issues.
I feel like the MSC's often want things both ways.
I feel that OP should be able to negotiate a new fee for the new work the MSC wants done.