There are primarily 3 reasons for PPC deviations:
1. Vendor Central vs API: Databases with Differently Timed Updates - Cleansing of Bot Traffic
Amazon will update and correct the data for Sponsored Products over the course of roughly 14 days after an event. For example, impressions and clicks will be cleansed by the traffic which resulted from Search Engines or Bots.
This data may be updated at slightly different times for Amazon's two channels (Vendor Central & API), which can lead to slightly different data outputs within the first week or so.
2. Lagged Allocation of Orders & Clicks
Sales will often only be attributed to the respective clicks with significant delays, as many customers will only buy the product several days after clicking on the ad. This Allocation can also be updated for the two channels at a different pace.
After around 7 days, most sales should be attributed to the respective clicks.
Recommended Time-frame for Optimizations: Two Weeks before Current Week
It is recommended to not consider the current week for any PPC analytics. This will also minimize the risk of falsely moving keywords to the Negative Keywords list, as many of its sales may not yet have been connected to the clicks of that keyword.
This is why the Sponsored Products Optimize tab offers a button which will directly set the time-frame for the two weeks before the current one (see picture below).
3. No Product Display Ads
Please remember that Amazon's API and thus Sellics only include Sponsored Products and Headline Search Ads.