Restrict your Sales or Account Manager to only their customer accounts in the Admin. When your Sales or Account Manager login to the Admin, they will only see the customer accounts for which they are the owner. All other customer accounts will be hidden from their view.
This setup will allow your Sales or Account Managers to also login as their customers and even purchase on their customers behalf.
How to Setup
Step 1: Create an Admin User for your Sales/Account managers. Give them the "assigner customer" permission.
Step 2: Import the Sales/Account manager as a new User on each of the their customer's accounts in the Admin.
Note: There are some fields in the csv that need special attention.
Email: Needs to be the email of the Sales/Account manager.
Username: Needs to be difference depending on email (Use the Customer's Account Code).
RoleId: The Role will determent the access the Sales/Account manager will have when logged in on under the customer's account. (Read more about customer role)
That's it! Now the Sales/Account manager can login under each of their customer's accounts on the storefront.
How to use
Step 1: Login on the admin dashboard
If the account has the permission referenced above, the following menu will appear as an option.
Step 2: On the current user account line, click on more options (...) and then on "Login".
The Sales/Account manager will now be logged into that customer's account on the storefront.
Good luck, let us know if there's something more to cover!