You'd need to make the Sales data the Primary data source and Agent name the Secondary data source. When using data blending, the primary data source needs to be the one with the most detail that you need, because everything from the secondary will be aggregated.
One complicating factor is if there are no rows in the sales data for an agent (like Charlie Brown), and you always want to show Charlie Brown in the worksheet, then you'd need to do some pre-processing to pad your data to always ensure there is always at least one row for each agent, such as via a cartesian query.
In order to join, the tables must come from the same data source. Therefore, when using two extracts, they cannot be joined, they must be blended. The reason for the asterisks is because there is a many to one relationship:
One way to maybe fix this (depending on the desired outcome) may be to switch the two sources so that the primary source is now the secondary and the secondary is the primary.
Hope this helps!