After being on the forum for 2 years (by tomorrow that is) I would say that there is no specific type or set of keywords to input in order to get the best search results but you have to be creative in exploring your list of product keywords in order to find more suppliers. The searches are basically based on what the supplier has listed on their profile, but sometimes you may discover that some suppliers do offer products not mentioned in their profile - so try using as many keywords as you can whether it be the brand name, the product type or category, part number or similar products.
Before our site was relaunched - search results would appear hierarchical starting with suppliers with 5 stars. But with such results oftentimes newer suppliers who may be just as good as the rated one will appear last most of the time. And may of our members would complain saying that they see the same set of suppliers every time they do a search.
I think classifying a supplier to be the best, 2nd best or not good at all may also be subjective since we all have different needs and each supplier offers something different :)
Our new SaleHoo user manual may help you utilize the directory to its fullest. To learn more about it (and download it too if you haven't) please visit the link below:
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Hope this helps.