First, you need a layout with this design:
---Sub summary when sorted by Client------
----Sub summary when sorted by purchase date------
Fields from Buying table go here
The layout would be based on the Buyings table.
This layout should be viewed in list view after sorting first by the client field specified in the first sub summary part and then also sorted by the Purchase date. Without correct sorting the sub summary parts will not be visible.
To limit the report to a specific set of records ( a given customer, a given date or range of dates, etc.) you perform a find and then sort the resulting records as I have already described.
Thanks as always PhilModJunk, I have a problem with the search part, when I enter search mode, it appears like the fields in the sub summary sections are not visible and so I cannot search for those values
You can use a different layout based on the same table occurrence to perform your search or you can use a script to perform the find.