The warehouse wins on everything it is measured on. It is faster, cheaper, more consistent, and it will refund you without an argument. Any honest case for buying from a person has to start there, because otherwise it is sentiment pretending to be reasoning.
What the warehouse is genuinely better at
Speed, price, predictability, and never having a bad week. If what you want is a known object delivered tomorrow, buy it from the warehouse. Nothing on this page is an argument against that.
What it cannot do
Sell you the only one. A warehouse stocks what it can stock repeatedly. Anything that exists once — the odd size, the discontinued thing, the object somebody's family kept for forty years — is not in it and cannot be.
Tell you about the thing. A listing generated from a catalogue knows the dimensions. It does not know that this particular one was reworked, or which of the two versions it is, or why the earlier ones are better. A person who has handled a hundred of them knows all three.
Answer a question you did not expect to ask. This is the underrated part. The useful information in a purchase is usually the thing you did not know to search for, and it arrives in conversation.
Be accountable in a way you can feel. A seller with a name and a store has something at stake in your parcel arriving well. That is a weaker guarantee than a refund policy and a stronger incentive.
Where the money goes, without the speech
Buying from a person means a larger share of what you paid reaches whoever made or found the thing. That is simply true, and it is not a reason to pay more for something worse.
The better framing is that you are often not paying more. For second-hand, odd-sized, out-of-production or handmade goods there is frequently no warehouse price to compare against — the alternative is not a cheaper version, it is nothing.
The honest trade
You accept slower. You accept that a seller is one person with a week that can go wrong. You accept that you may have to ask a question rather than read an answer.
In return you get access to the enormous category of things that cannot be mass-produced, and you get to deal with somebody who knows what they are selling.
Questions people ask
Is buying from a person riskier?
The transaction is not — the money is held until it arrives, and a faulty item is returnable for 7 days whatever the store's policy. The variability is in speed, not in safety.
Am I paying a premium for the story?
Sometimes, and you should decline when that is all you are paying for. The useful test is whether the object would still interest you with no story attached.
How do I tell a real small seller from a reseller pretending?
Ask about the thing. Specific answers come from specific knowledge. And both are allowed here — the point is that the listing should not claim to be the other.
More: buying handmade work, handmade or resold, finding a seller you can trust, why handmade costs more.