So we are using Teams and using the Sharepoint site that gets created more and more.
We created a Team, then invited some external guests to the team. They can interact with the team just fine. We went to the Sharepoint Online site and verified that they have RO access. Well one of our test accounts, a Gmail account can access the site, but has Edit permissions to the site. This is not what we want. Is there another permission somewhere that we need to check? Thanks!
1. The group permissions, when a user gets added to the team as a guest they get added to the underlying Office 365 group. There is not a way to give them read only access to the group. By adding them to the group they have edit access to the SharePoint site.
2. SharePoint site permissions - you can give access just to the underlying SharePoint site. If you removed the test user from the Microsoft Team you will should see that they just have read only access to the site.
I don't know of any way to give Read Only access to the underlying SharePoint site whilst still being a guest in the Microsoft Team.
If the user was a guest in the Team they all have edit rights not RO to the underlying SharePoint site by default. However you can as an owner change the site level permissions of the SharePoint members group that contains the Office 365 members group to make it read only. But you cannot separate guests from members In regards to the underlying SharePoint access only owners vs Members(guests) can have a difference.