Hey @Daniel_M! Welcome to Webflow!
So a lot of this really depends on what level of “integration” you want.
Looking at the har website they have some developer resources by the look of it. And you may be able to just embed an iframe or something.
If they have an API, you may be able to use something like zapier or integromat to take the data out of the MLS, then create Webflow CMS items. From there you can style and setup however you would like in Webflow.
Hope that helps somewhat. 