I would like to activate an automatic 5% discount for all logged in customers.
The shop itself is 10+ years old, has been updated/migrated from 1.3->1.6->1.7.8 and therefore has the Customer Groups Default/Guest/Visitor. I know that now it is Visitor/Guest/Customer, but I have not figured out how the old classification corresponds to that.
As I'm not sure to which of these groups should I add the 5% discount (I tried the default one, but it gives a discount to a guest user as well), the easiest way would probably be to create a new group and assign the discount there? But for that, I need to get info about which customers actually have an account, so I can add only them to this group.
If the info is relevant, then one-page check-out is not possible due to the theme.