Economic parasite; he
buys something from its
source and sells it to you for more than he paid for it. You pay for the
convenience of not having to go to the source.
Often instead of selling to you, he sells to another middleman, who then marks up the price a bit more and sells it either to you or to another middleman, who marks up the price then sells it to you.
Note that there is a lot of marking up going on here.