Partners auto-created when you create a user should have customer=False and supplier=True

base_usability/__init__.py

@@ -1,5 +1,6 @@
 # -*- coding: utf-8 -*-
 
+from . import users
 from . import partner
 from . import company
 from . import mail

base_usability/users.py

@@ -0,0 +1,20 @@
+# -*- coding: utf-8 -*-
+# Copyright 2018 Akretion (Alexis de Lattre <alexis.delattre@akretion.com>)
+# License AGPL-3.0 or later (http://www.gnu.org/licenses/agpl).
+
+from odoo import models, api
+
+
+class ResUsers(models.Model):
+    _inherit = 'res.users'
+
+    @api.model
+    def default_get(self, fields_list):
+        res = super(ResUsers, self).default_get(fields_list)
+        # For a new partner auto-created when you create a new user, we prefer
+        # customer=False and supplier=True by default
+        res.update({
+            'customer': False,
+            'supplier': True,
+            })
+        return res