Best practices normally promote excluding some users from your dynamic audiences. This is typically seen when you prevent your ads from being shown to recent purchasers. If they've recently purchased your product or services, they may be less likely to return and you will effectively waste money advertising to them.
In order to best deploy this strategy, you'll first need to understand how the exclusion logic works when it comes to dynamic audience creation.
Option 1 - Group Exclusion
The first option that Facebook attempts to exclude on is by the group that the purchased product was a member of. This is driven by the presence of the 'item_group_id" field in your feed.
For example, consider that you sell various colors and sizes of a specific type of shirt. All of these variations are split out as separate, unique products in your feed. However, they all share the item_group_id of 123.
When a user purchases an item from this group, Facebook will then apply whatever exclusion logic in place against that group only. So if you have an audience that excludes users who have purchased in the last 14 days, this user will not see any other shirts from group 123 for those 14 days.
In this scenario, depending on your campaign and audience setup, the user in question may continue to see other products (pants, shoes, etc) from your catalog outside of the now-excluded group.
Option 2 - Product Exclusion
The group-level exclusion listed above is the default behavior with Facebook DPAs. However, it requires 'item_group_id' to be a valid field in the feed. If this field does not exist, Facebook will then fall back on to product-level exclusion.
Using the same example as above, the user who bought a shirt will not see that same exact shirt for the 14 day "excluded purchasers" window. However, depending on his activity on the site and the campaign setup, they may see other similar shirts in addition to the rest of your product catalog.
In most cases, the group-level exclusion is the preferred behavior here. In order for it to operate as expected, we suggest ensuring that your feed contains the item_group_id field and subsequent values. While this field is not required by Facebook to run DPAs, it does typically result in the best exclusion logic available.