If we take as granted that Accenture and similar do low-quality work as judged by tech experts yet have a large business with a mostly-positive general-public reputation... how is some poor middle manager or non-technical executive in a company that finds themselves needing a technology solution supposed to pick a good vendor? Go with someone big an well-known? Nope, that's shit, apparently. Go with someone small and unknown? That seems even worse - how are they going to be qualified to judge the bidders?

No, I don't think someone small is necessarily worse -- on the contrary, I think someone small(ish) and local (which makes them less unknown) may well be better. You choose them the same way anyone chooses any vendor or contractor: Ask your friends. Like, if you own a somewhat older car, so you're not willing to pay the "Manufacturer's Seal of Approval" surcharge for having it serviced -- then you'd ask around aming friends and acquaintances about which garages they'd recommend or warn you to stay away from, wouldn't you? And in a sibling comment, someone talks about choosing a plumber. You'd ask other homeowners, wouldn't you?

Your middle manager or non-technical executive presumably doesn't live in a sealed jar. They know other middle managers and non-technical executives, personally and/or professionally. So they use their network, ask colleagues about their experiences with local small-to-midsize providers of such services. Why "small(ish)" or "small-to-midsize", you ask? Because then you're a) negotiating on more of an even footing than you'd be with a "Big 6" firm that has the expertise to put together Power Point decks to bamboozle you, and the resources to bury you in court after the project becomes a clusterfuck. And why am I harping on "local"? Because then their reputation is also local, so you can find out about them via your network. And then you will also contribute your part to it; they won't want you to become that guy who warns his colleagues off from them.

Citation needed. Ideally pointing out -informed- general public reputation; after all, we had a person elected president due in large part to perceptions from the every man of his business acumen despite running -casinos- into the ground.

If you're hiring a company to do something you don't know how to do, you might not even know where to find informed opinions.

If I was going to hire a plumber I'm sure there are some places that all the good plumbers know are scam artists, but I have no idea who the good plumbers are.