Check if username exists before attempting to create a domain

We've encountered this error when cloning a domain name:

I am pretty sure it would output the same error when not cloning, but just creating a new virtual server provided there was already same username in the system. So instead of throwing error to the screen (and thus confusing inexperienced end-users) wouldn't be more appropriate to automatically modify duplicate username by adding some digits like, in our case, clone0, clone1, clone2, etc? Generally it's a good practice to leave to end-users as few errors as possible.