Thank you for your suggestions. The exclusion of individual departments is something that I would love to do as well, but have not been able to figure out yet. Much of what I do in order to make my search so much more functional than Amazon's is trying to find undocumented features in Amazon's programming interface. So it is possible that with time I will discover how to exclude individual departments. For now I only figured out how to exclude product groups and select multiple departments at once (none of those things are possible on Amazon's website). So stay tuned. Your second suggestion is interesting, I will think about a way to implement it, although UI may be challenging. For now I would suggest leaving the results sorted by relevance and use the min# of reviews and min user rating sliders to only display the results that are highly rated. Thanks again for writing. I am glad you are finding my site useful and I would appreciate if you spread the word.
I can see how the second suggestion might be a problem, as you'd probably have to pull down all the search results, scan through them to get the relevancy and the rating, calculate the weighted sort rank, and then sort and paginate them. Fine if the search returns a few hundred items, but a larger result set than that would probably be unmanageable. For now, I usually do exactly what you suggest.