When realtors shop for a website, one of the most common questions is "does it have an MLS feed". The question is usually a proxy for a different question, "will it display my listings on my site". These two things are related but they are not the same, and understanding the difference will save you a lot of frustration.
The MLS feed is the data
An MLS feed is a technical connection between your website's backend and your board's database. Through that connection, your site can read listings data, refresh it periodically, and store a local copy. The feed itself does not produce a webpage. It just provides raw structured data: addresses, prices, beds, baths, photos as URLs, descriptions, status fields.
The feed has nothing to do with what the listings look like on your site. It is just plumbing. A well configured feed updates listings every 4 to 24 hours, handles new listings, handles status changes (active to pending to sold), and keeps your local data in sync with the board.
The listings display is the presentation
The listings display is how your website renders that data for visitors. The same MLS feed can power dozens of different listing displays, ranging from beautiful editorial layouts to ugly iframe widgets.
This is where the real quality variation between realtor websites lives. Two agents can have the same MLS feed pulling the same data, and end up with wildly different listings pages. One renders as a beautiful grid with high resolution photos, smart filtering, fast performance, and proper SEO markup. The other renders as a 2012 iframe that loads slowly, has no mobile layout, and is completely invisible to Google.
The iframe widget trap
Many realtor website builders solve "listings display" by embedding a third party iframe widget. The widget connects to the MLS feed on its server, and shows your listings on your site via an iframe.
This is the worst case. It looks like your site has listings, but technically the listings are not on your site at all. They are on the widget provider's domain, embedded as an iframe. Three problems result.
Zero SEO benefit. Google does not credit your site for content inside an iframe. All the listings you display are invisible to Google as far as your site's content goes.
Poor performance. Iframe widgets are usually slow because they have to load a separate document inside your page.
No design control. You are stuck with whatever the widget provider's CSS looks like.
The right way is to ingest the MLS feed into your site's database, and render the listings as native pages on your domain. Each listing becomes a page like yoursite.com/listings/123-oak-street. Google indexes it. The SEO benefit accrues to your domain. Your design system controls the presentation.
What to ask when shopping for a website
Three questions. Their answers tell you everything.
"How are listings rendered on my site?" If the answer is "via an embedded widget", run. If the answer is "as native pages stored on your site, generated from the MLS feed", you are on the right track.
"Does each listing have its own URL on my domain?" If the answer is no, listings provide zero SEO value to you. If yes, every listing is its own indexed page.
"Can I see structured data (schema.org) markup on a sample listing page?" Right click on a listings page, view source, search for "Residence" or "Offer" or "schema.org". If you find it, the site is doing SEO right. If you do not, listings will rank poorly.
Why this matters more than you think
Each listing page is a chance to rank for hyperlocal long tail queries. "123 Oak Street Mississauga" is a search someone will type when they are seriously evaluating the property. If your listing page exists on your domain with proper schema, you can rank for that search and capture a high intent visitor.
If your listings live in a third party widget, you get none of that. Your competitor whose listings live on their domain gets all of it.
The MLS feed is just the start. The display layer is where the SEO compound effect actually happens.