Problems with users not logged in viewing a cart

We have inhertied a drupal site (5.x) with eCommerce module that, when a user isn't logged in, displays the same cart and notes to every guest user until they login.

Obviously this isn't ideal. I have checked the module code and I assume that this is taken by the session id, however when checking the database entries the user id associated is always 0.

Can anyone shed any light?