Is the report from another database? If so, see if you can get that databases key field included in the report. Then you can create a field in your QB table called 'Key Field for Import', make that unique and import on that field.
If you don't have a key field on the export, then the only way I have found to do this is 'create' my own key field.
I made an excel sheet template, which looked exactly like my sheet I want to import, except I add a column on the end called 'Key Field'. This key is some combination of your columns that will definitely make it unique. Maybe it is Date+Client+Amount. In that example, you would get a unique string provided that the client never paid you the same amount twice on the same date.
Then every time I goy my excel sheet, I simply quickly copied it to my template, and the import my template matching key field.
