I think the point is that Craigslist itself is supposed to connect buyers and sellers, and he's inserting himself aggressively between them for profit, adding no real value.
1) He retakes clear photos of the merch at a variety of angles - something that many craigslist postings lack
2) He himself has a threshold of quality, and inspects the product before picking it up from the original seller - I would much rather trust a guy who buys 10 cordless drills a week on craigslist to know the drill is bad, than relying on my limited knowledge of cordless drills and their common defects.
I'm willing to pay a few extra bucks for his vetting.
To the seller: I'm going to make probably $100 on this washer in a couple days by Windexing it and taking some good photos. That's your fee for my pickup and selling "service."
To the buyer: I bought this washer a couple days ago for $100 less. That's your fee for my delivery and vetting "service."
I'd like to know how much is e.g. Apple paying Foxconn for each iPhone, doesn't mean I think they're wrong for not telling me.
(Purely hypothetical example, I don't buy stuff from Apple)
People who do not have time to check craigslist's free section around the clock are able to buy items at less than retail price.