If your seller cannot login to thier account.
Please make sure that they are either going to the Seller Login you have set up for your page or to the Customer Login at the top right corner of ShowingSuite.com.
You will also want to make sure the username doesn't have any wierd characters($, %, & !) and the password is atleast 6 charaters long.
A good test for this is to copy the username and password you have set for them and login to their account. Remember you will need to log out of your Showing Suite account First!