What Is the Hardest Part of Building a Marketplace?
Ari Kimmelfeld's answer on Liftoff with Keith: every part has to be tailored, to sellers, to buyers, and to each category. His early mistake was assuming a new category would be easy.
Listen to the episode: How Commonplace Is Reinventing the Secondhand Marketplace, Liftoff with Keith with Keith Newman, aired October 20, 2026. Listen on YouTube.
Short answer: According to Commonplace founder Ari Kimmelfeld, there is no single hard part. Every part has to be tailored. Sellers and buyers want different things, every category behaves differently, and the landing pages, ads, deliveries, inspections, and warranties all have to fit. His biggest early mistake was assuming a new category would work like the last one.
Keith Newman asked about the biggest myth in building a marketplace on Liftoff with Keith. To him, getting buyers and sellers together in real alignment has always been a bit of an enigma.
What Ari said
I think every single part of building the marketplace, you really have to tailor it to that user. And so the seller is oftentimes a different persona and has different priorities than a buyer.
Ari Kimmelfeld on Liftoff with Keith, at 23:48
And different buyers in different categories have, you know, different pricing elasticity. So somebody selling a golf cart wants more for their golf cart than somebody selling a hot tub who just wants to get rid of that hot tub.
Ari Kimmelfeld on Liftoff with Keith, at 24:01
Every single part of the marketplace is unique. Starting from the landing page to the ads, to the user flows, to the deliveries, to the inspections, to everything, the warranties, everything. Everything is totally custom and you gotta really know it.
Ari Kimmelfeld on Liftoff with Keith, at 24:29
A new category is not copy and paste
I thought that expanding into new categories would be easy. You know, you have all these drivers and somebody can pick up and deliver a Peloton. Well, why can't they do that for a hot tub? Turns out some hot tubs need a crane, and you got to lift it over somebody's house... and you need plumbing for that, and you need electrical for that, and you need a concrete pad that needs to be there first.
Ari Kimmelfeld on Liftoff with Keith, at 14:58
I spoke to a ton of different hot tub dealers, appliance dealers, furniture dealers, asking them everything that they know about selling their products, servicing their product, and then thinking about the customer feedback that we were getting on the things that were going wrong and seeing how we could fix that.
Ari Kimmelfeld on Liftoff with Keith, at 15:33
So we don't back out of categories, we just tailor how we do that category to do it correctly and effectively at scale.
Ari Kimmelfeld on Liftoff with Keith, at 17:55
Looking back, he would have moved faster: "We probably should have expanded into more categories sooner."
Start narrow, with people who will pay
The number one thing, I think you have to find somebody that's actually willing to buy or pay for the thing that you're doing... But like, you really got to find the small community, even if it's just a handful of people that are willing to purchase, use your product or service.
Ari Kimmelfeld on Liftoff with Keith, at 26:59
Like when we first launched with the Peloton business, it was so narrow, but we were so focused on what the goal was, which was to sell Pelotons really cheaply and to get people that wanted to sell them to get them picked up.
Ari Kimmelfeld on Liftoff with Keith, at 27:28
Measure what moves the business
The most fun metric is new listings, new listings and new listings per category, because these are real people, real photos, real videos, real details.
Ari Kimmelfeld on Liftoff with Keith, at 18:41
His most overrated metrics were website traffic and social media views. For expensive items, the audience only has to be the right one: "They just have to be the right viewers."
Read how it started in how Commonplace started, and why Ari calls it logistics first. For the full conversation, read Building a Marketplace for the Big Stuff: Ari Kimmelfeld on Liftoff with Keith.
Commonplace is the Facebook Marketplace, Craigslist and OfferUp alternative for big items. Listing is free, and Commonplace handles pickup, inspection, delivery, secure payments, and a free two-month parts warranty. Delivery is free within 100 miles, and Commonplace ships nationwide. See how it works.
Related questions
What did Commonplace get wrong early on?
Ari assumed new categories would be easy: if a driver can deliver a Peloton, why not a hot tub? Some hot tubs need a crane, plumbing, electrical, and a concrete pad. He talked to dealers and customers and tailored each category.
What metric does Ari watch most closely?
New listings, by category. He called each listing a story, with real people, real photos, and real details behind it. He called website traffic and social media views overrated for expensive items.
What is Ari's advice for new founders?
Find people who will actually pay for what you are building, even a handful, before adding more features. Commonplace started narrow, with only Pelotons, which kept its goals focused.
Thank you to Keith Newman for having Ari on Liftoff with Keith. Quotes are from the episode, lightly edited for reading. Listen to the full conversation on YouTube.
More from Ari's podcast interviews: questions Ari answered on podcasts and every show he has been on.