I’m fairly new to this but here it goes…
You could create three roles in security suite.
Manager can access the most stuff.
sales can see all their own stuff and dealers stuff.
dealer can access only stuff he owns.
Step 1 - Create roles for each and specify permissions. Assign users to the roles individually.
Manager - All
Sales - Group
Dealers - Owner
Step 2 - Create a security group and add all three roles, untick inheritable.
You should have what you need from there and tweak to your liking. You can assign permissions quickly by clicking the column titles e.g. edit, view, list, etc.