Amazon's search, filter and sorting tools do not produce accurate results. It appears as if items are presented out of order in order to favor certain manufacturers and/or suppliers over others. I have reported it to Amazon in the past and they have been able to reproduce my results but offered no explanation.
The example below is typical of the results I have found on other searches. It is NOT a onetime anomaly.
I entered "Smoke Detector" in the search field at Amazon.com
I then filtered by "Prime Eligible"
I then filtered by 4 stars or greater (reviews)
I then selected "Tools and Home Improvement" as the category
Finally I sorted by price, low to high.
The results were smoke detectors priced in the following order:
I can only conclude that Amazon is favoring certain manufacturers and/or suppliers over another and moving their products higher on the search/sort/filter results list.