What is the difference between a web store and a marketplace?

There are many differences, all very significant. It’s important to understand these differences so you can build your business plan accordingly. I also want to emphasis here, for many online businesses, it isn’t an either/or choice. Many, many companies operate more than one online sales channel. You may decide you want to sell on marketplaces and on your own website.

Difference /2/ you have to bring an audience

Marketplaces spend a lot of money driving traffic to their website. When you own the site, you have to drive the traffic. It gets harder than that. “Just traffic” isn’t enough. It has to be targeted traffic. This means that the people that come to your site are interested in what you sell, and are ready to buy. There are many ways to drive traffic but in the beginning it almost always requires spending money.
Advertising is usually the fastest way to bring buyers. Other traffic drivers include social media, finding influencers to write about, or talk about, or post about, your products, and search engine optimization (SEO). SEO takes time before it will drive an audience and a lot of content, so that leaves largely paid options for brand new stores. Over time, you an add email marketing, referral marketing and affiliate programs to drive sales but these are not powerful tools until you have actual sales volume rolling in.

Difference /2/ you have to earn their trust

The customer on the marketplace buys from you primarily because they trust the marketplace to have their backs. You are trading on their brand trust, not your own. Even with this level of support, sellers who don’t have a lot of positive customer feedback experience slower sales until they build up good reviews. When you have your own store you have to build trust and appear trustworthy from your very first day. This is a lot of work.
Your store must appear, and be, trustworthy. This means it operates well, looks great, is well organized and has well-written policies regarding shipping, returns, and privacy. Customers must also be able to contact you. In most cases, stores that do not publish a local address and phone number will appear less trustworthy and not do well. Spelling and grammar must be impeccable. Product photos need to be clean and consistent. Product descriptions should be original and well written. Your site must be secure. This all marks just the beginning of building trust.