No, that assumes perfect market information. Middlemen can provide benefit by allowing people to offload research and reputation tracking to a third party that they trust, allowing them to invest time and effort in that one entity instead of a bunch of smaller ones.

For example, do you buy off Amazon or NewEgg, Best Buy, etc or do you just use Craigslist, Ebay, the local paper, or even the local flea/market swap meet for electronics? You can probably find stuff for half as much or even less at some of those locations, but it might cost you a lot in research time or lost money in the end...