Specifically warn about some shredders

src/pretix/base/shredder.py

@@ -74,6 +74,13 @@ class BaseDataShredder:
         """
         raise NotImplementedError()  # NOQA
 
+    @property
+    def tax_relevant(self):
+        """
+        Indicates whether this removes potentially tax-relevant data.
+        """
+        return False
+
     @property
     def verbose_name(self) -> str:
         """
@@ -216,6 +223,7 @@ class AttendeeNameShredder(BaseDataShredder):
 class InvoiceAddressShredder(BaseDataShredder):
     verbose_name = _('Invoice addresses')
     identifier = 'invoice_addresses'
+    tax_relevant = True
     description = _('This will remove all invoice addresses from orders, as well as logged changes to them.')
 
     def generate_files(self) -> List[Tuple[str, str, str]]:
@@ -269,6 +277,7 @@ class QuestionAnswerShredder(BaseDataShredder):
 class InvoiceShredder(BaseDataShredder):
     verbose_name = _('Invoices')
     identifier = 'invoices'
+    tax_relevant = True
     description = _('This will remove all invoice PDFs, as well as any of their text content that might contain '
                     'personal data from the database. Invoice numbers and totals will be conserved.')
 
@@ -312,6 +321,7 @@ class CachedTicketShredder(BaseDataShredder):
 class PaymentInfoShredder(BaseDataShredder):
     verbose_name = _('Payment information')
     identifier = 'payment_info'
+    tax_relevant = True
     description = _('This will remove payment-related information. Depending on the payment method, all data will be '
                     'removed or personal data only. No download will be offered.')
 

src/pretix/control/templates/pretixcontrol/shredder/index.html

@@ -25,7 +25,8 @@
         <strong>
             {% blocktrans trimmed %}
                 It is within your own responsibility to check if you are allowed to delete the affected data in your
-                legislation, e.g. for reasons of taxation.
+                legislation, e.g. for reasons of taxation. In many countries, you need to keep some data in the live
+                system in case of an audit.
             {% endblocktrans %}
         </strong>
         {% blocktrans trimmed %}
@@ -57,6 +58,15 @@
                         </label>
                         <div id="payment_{{ p.provider.identifier }}" class="panel-collapse in">
                             <div class="panel-body">
+                                {% if shredder.tax_relevant %}
+                                    <div class="alert alert-legal">
+                                        {% blocktrans trimmed %}
+                                            We recommend not to remove this data because you might need it in case
+                                            of a tax audit.
+                                        {% endblocktrans %}
+                                        <div class="clear"></div>
+                                    </div>
+                                {% endif %}
                                 {{ shredder.description|safe }}
                             </div>
                         </div>