My biggest complaint about MCS is akin to keyword spamming on ebay. However, rather than include terms like “CGC it!” for raws or “Like CGC” for other companies, they use “1st Series." For example, let’s say I want to search for a copy of "Fantastic Four #1." I don’t get listing just for copies of that book, I get EVERY issue between 1-416 that MCS has listed, hundreds and hundreds of listings, pages of books besides #1 because they all say “1st Series” in the title and the search engine reads the “1”.
I know I can run a filtered search minus MCS, but that’s a PITA to me.