This is a common question.
The big difference between a page and a post
by default, is that a page
cannot be archived (you cannot have a list with all the pages for a given category, for example) and a post can.
Why, then using a page, if by default has less capabilities?
Archiving is not always a great idea, for example, how may you "archive" your contact page? or your "about us" page?
You can have a category called: "Services" and then create all posts within that category.
Most people though prefer to create pages for services. Why? Because they don't understand how Wordpress works OR, they use plugins that
ALTER the default WordPress behavior.
Also
be aware, that
posts, are,
BY DEFAULT, listed in the blog default page archive. Meaning, that if you are planning to blog in that site at some point, if you place the services as posts, they will show up as blog posts, which could be a little bit weird.
This is also, why most people prefer to list services as pages instead of posts if they are planning on creating a blog in the future.
Which is the most "optimal" method then?
There are two alternatives:
1. Creating pages and activating a taxonomy (categories for example), then you will have the archiving functionality for pages. You can do this with a plugin like
https://es.wordpress.org/plugins/add-category-to-pages/ or with a little bit of code in the functions.php, although, if you are asking this, I think that the plugin is a better idea
2. The "
PRO" way, by creating a
Custom Post Type (CPT) called Services and adding there all services. You could even define some custom fields (for example the price), and show them up in a special way by templating the CPT page (you can do this with Gutenberg and Toolset Types + Toolset Blocks plugins fairly easy).
Or just create some pages, and forget about archiving. The only advantage of archiving is the capability of auto-listing anywhere in your site based on the taxonomy selected (the category for example) or the CPT type.
Other than this, there are no differences between pages and posts. SEO differences are pure bullshit.