Best Match is terrible.
I believe it is arguably illegal - because of misrepresentation
* buyers are led to believe they are getting a balanced presentation of goods for sale and they are not
* sellers are led to believe they are buying an even opportunity to sell their goods ~ yet I have seen many items finishing on Page 4 of listings with many items finishing the next day appearing on Page 1 of listings, for example. You can find numerous examples of sellers who paid for "Featured Item" listings who nevertheless fall into this trap.
Beyond that, BM sucks completely and thoroughly.
* for finding, it has the opposite effect that it is supposed to have - it is counterproductive to give specific or unique descriptions of your product
Think about it: there are 50,000 paintings on eBay, all of these now try to use the same 3-5 "mandatory" key words (original, painting, by, abstract, oil, nude) and mix 'n' match with maybe a dozen other keywords that do not appear to give you a negative BM effect (tree, landscape, canvas, modern, surreal, etc...).
In effect, (in the art category) if you describe your listing with anything beyond the most banal words, you are penalized and go to the back.
* Free Shipping overpowers all other factors in BM - OK we get it - eBay thinks it deserves to make a cut on $ being spent on shipping. I get it, it is still coercion.
* recped's theory that if BM disadvantages one seller the advantage is gained by another is mistaken. Many buyers will simply not buy if they do not find what they are looking for. If sellers are forced to use lame generic titles so as not to disadvantage themselves by including a more specific description, then the buyer will just not buy. (granted in some categories where for all I know you can have 50,000 listings with one seller like stamps, books, postcards or whatever, the descriptions will continue to be more specific and varied even under BM)
* using a creative title to incite a purchase by a buyer BROWSING is made nearly impossible
* BM encourages ridiculous situations like the "New Art Trend" on eBay of artists painting with "acrylics and oil" just so that sellers can include the word "oil" in their listings. I am sure this is repeated across eBay in various forms. This cheapens and further damages the reputation of all eBay sellers
I could go on and maybe will... later:-)