First try making tolerance not costly.

A new configuration setting was introduced: tolerance_is_costly
If set to false, article tolerance values do not count for total article price as long as the order is not finished.
This reduces the negative effect on using tolerance for the user.

app/models/group_order.rb

@@ -29,13 +29,18 @@ class GroupOrder < ActiveRecord::Base
   named_scope :finished, lambda { {:conditions => ["order_id IN (?)", Order.finished_not_closed.collect(&:id)]} }
   
   # Updates the "price" attribute.
-  # This will be the maximum value of an open order or
-  # the value depending of the article results.
+  # Until the order is finished this will be the maximum price or
+  # the minimum price depending on configuration. When the order is finished it
+  # will be the value depending of the article results.
   def update_price!
     total = 0
     for article in group_order_articles.find(:all, :include => :order_article)
       unless order.finished?
-        total += article.order_article.article.fc_price * (article.quantity + article.tolerance)
+        if Foodsoft.config[:tolerance_is_costly]
+          total += article.order_article.article.fc_price * (article.quantity + article.tolerance)
+        else
+          total += article.order_article.article.fc_price * article.quantity
+        end
       else
         total += article.order_article.price.fc_price * article.result
       end

app/views/ordering/my_order_result.haml

@@ -78,7 +78,10 @@
                 - tolerance = goa.tolerance
                 - result = goa.result
                 - if @order.open?
-                  - sub_total = oa.price.fc_price * (quantity + tolerance)
+                  - if Foodsoft.config[:tolerance_is_costly]
+                    - sub_total = oa.price.fc_price * (quantity + tolerance)
+                  - else
+                    - sub_total = oa.price.fc_price * quantity
                 - else
                   - sub_total = oa.price.fc_price * result
               - else

app/views/ordering/order.rhtml

@@ -32,9 +32,12 @@
           </tr>
 				<%-
 				order_articles.each do |order_article|
-	                article_total = @price[i] * (@tolerance[i] + @quantity[i]);
+                    if Foodsoft.config[:tolerance_is_costly]
+                        article_total = @price[i] * (@tolerance[i] + @quantity[i])
+                    else
+                        article_total = @price[i] * @quantity[i]
+                    end
 	                total += article_total
-
         -%>
           <tr class="<%= cycle('even', 'odd', :name => 'articles') %>" valign="top">
               <td class="name">
@@ -107,14 +110,23 @@
 <script type="text/javascript">
 //<![CDATA[
     // preset data
-<% for i in 0...@price.size -%>
+<% if Foodsoft.config[:tolerance_is_costly]
+       for i in 0...@price.size -%>
     addData(<%= @price[i] %>, <%= @unit[i] %>, <%= @price[i] * (@tolerance[i] + @quantity[i])%>, <%= @others_quantity[i] %>, <%= @others_tolerance[i] %>, <%= @used_quantity[i] %>, 0);
-<% end -%>
+<%     end
+    else
+       for j in 0...@price.size -%>
+    addData(<%= @price[j] %>, <%= @unit[j] %>, <%= @price[j] * @quantity[j]%>, <%= @others_quantity[j] %>, <%= @others_tolerance[j] %>, <%= @used_quantity[j] %>, 0);
+<%    end
+    end%>
     setGroupBalance(<%= @availableFunds %>);
 
     // localization 
     setDecimalSeparator(",");
 
+    // configuration
+    setToleranceBehaviour(<%= Foodsoft.config[:tolerance_is_costly] %>);
+    
     // initialize javascript
     updateBalance();    
 //]]>

public/javascripts/ordering.js

@@ -8,6 +8,7 @@
 var modified = false    		// indicates if anything has been clicked on this page
 var groupBalance = 0;			// available group money 
 var decimalSeparator = ".";		// default decimal separator
+var toleranceIsCostly = true; // default tolerance behaviour
 
 // Article data arrays:
 var price = new Array();
@@ -22,6 +23,10 @@ function setDecimalSeparator(character) {
 	decimalSeparator = character;	
 }
 
+function setToleranceBehaviour(value) {
+    toleranceIsCostly = value;
+}
+
 function setGroupBalance(amount) {
 	groupBalance = amount;
 }
@@ -98,7 +103,11 @@ function update(item, quantity, tolerance) {
 	}
 	
 	// update total price
-	itemTotal[item] = price[item] * (Number(quantity) + Number(tolerance));
+    if(toleranceIsCostly == true) {
+        itemTotal[item] = price[item] * (Number(quantity) + Number(tolerance));
+    } else {
+        itemTotal[item] = price[item] * (Number(quantity));
+    }
 	$('price_' + item + '_display').update(asMoney(itemTotal[item]));
     
     // update balance