diff --git a/addons/crm/wizard/crm_lead_to_opportunity.py b/addons/crm/wizard/crm_lead_to_opportunity.py
index a0a0874367d..b987bce5386 100644
--- a/addons/crm/wizard/crm_lead_to_opportunity.py
+++ b/addons/crm/wizard/crm_lead_to_opportunity.py
@@ -174,10 +174,10 @@ class Lead2OpportunityMassConvert(models.TransientModel):
     user_ids = fields.Many2many('res.users', string='Salesmen')
     team_id = fields.Many2one('crm.team', 'Sales Team', index=True)
     deduplicate = fields.Boolean('Apply deduplication', default=True, help='Merge with existing leads/opportunities of each partner')
-    action = fields.Selection([
+    action = fields.Selection(selection_add=[
         ('each_exist_or_create', 'Use existing partner or create'),
         ('nothing', 'Do not link to a customer')
-    ], 'Related Customer', required=True)
+    ], string='Related Customer', required=True)
     force_assignation = fields.Boolean('Force assignation', help='If unchecked, this will leave the salesman of duplicated opportunities')
 
     @api.onchange('action')
diff --git a/addons/sale/wizard/payment_acquirer_onboarding_wizard.py b/addons/sale/wizard/payment_acquirer_onboarding_wizard.py
index 3f932838183..01ffed669d3 100644
--- a/addons/sale/wizard/payment_acquirer_onboarding_wizard.py
+++ b/addons/sale/wizard/payment_acquirer_onboarding_wizard.py
@@ -14,12 +14,9 @@ class PaymentWizard(models.TransientModel):
     def _get_default_payment_method(self):
         return self.env.company.sale_onboarding_payment_method or 'digital_signature'
 
-    payment_method = fields.Selection([
+    payment_method = fields.Selection(selection_add=[
         ('digital_signature', 'Online signature'),
-        ('paypal', "Pay with PayPal"),
-        ('stripe', "Pay with credit card (via Stripe)"),
-        ('other', "Pay with another payment acquirer"),
-        ('manual', "Custom payment instructions"),
+        ('paypal',),
     ], default=_get_default_payment_method)
     #
 
diff --git a/addons/sale_crm/wizard/crm_opportunity_to_quotation.py b/addons/sale_crm/wizard/crm_opportunity_to_quotation.py
index 6a4dabb151b..5bb95af10b7 100644
--- a/addons/sale_crm/wizard/crm_opportunity_to_quotation.py
+++ b/addons/sale_crm/wizard/crm_opportunity_to_quotation.py
@@ -24,10 +24,7 @@ class Opportunity2Quotation(models.TransientModel):
             result['lead_id'] = active_id
         return result
 
-    action = fields.Selection([
-        ('create', 'Create a new customer'),
-        ('exist', 'Use an existing customer')
-    ], 'Quotation Customer', required=True)
+    action = fields.Selection(string='Quotation Customer')
     lead_id = fields.Many2one('crm.lead', "Associated Lead", required=True)
 
     def action_apply(self):
diff --git a/odoo/fields.py b/odoo/fields.py
index 44cbc97d9d4..3a6824433cc 100644
--- a/odoo/fields.py
+++ b/odoo/fields.py
@@ -2048,6 +2048,11 @@ class Selection(Field):
             if 'selection' in field.args:
                 selection = field.args['selection']
                 if isinstance(selection, list):
+                    if (
+                        values is not None
+                        and values != [kv[0] for kv in selection]
+                    ):
+                        _logger.warning("%s: selection=%r overrides existing selection; use selection_add instead", self, selection)
                     values = [kv[0] for kv in selection]
                     labels.update(selection)
                 else:
@@ -2055,8 +2060,10 @@ class Selection(Field):
 
             if 'selection_add' in field.args:
                 selection_add = field.args['selection_add']
-                assert isinstance(selection_add, list)
-                assert values is not None
+                assert isinstance(selection_add, list), \
+                    "%s: selection_add=%r must be a list" % (self, selection_add)
+                assert values is not None, \
+                    "%s: selection_add=%r on non-list selection %r" % (self, selection_add, self.selection)
                 values = merge_sequences(values, [kv[0] for kv in selection_add])
                 labels.update(kv for kv in selection_add if len(kv) == 2)