Sage 100

We have a client that imports vendor payments through manual check entry. The problem is that the file they have could include checks that have already been imported. Apparently there is no way to prevent the source file to be produced b check date. According to Sage we need some perform logic that will check the check history header file to see if check exists during the import function.
Has anyone written perform logic like this or have a suggestion to prevent duplicate checks from being imported.
Thanks