This View can be used to find out if you imported the correct commission data or if you imported the same data twice. If you want to trash all data that you imported for a supplier or for all suppliers you can also choose to trash some items on the Import data page

Top Menu >> Import Data >> ...More >> View Imports

It will list out your imports and will sort them out based off of Supplier and import method. Click View items will filter out all items imported for that Supplier.

Click ...More >> Trash these items

If you suspect you imported data twice for a supplier, you can sort by Supplier by clicking on the Supplier header. One thing to note is that this View will keep a historical log of every import done, so only rows with items will actually have commissions data.