why not to try showing only '-own document?

hi

try to make groups for each sale Type , like privilage A, B and C, those privilages refers to sale kind.
now in python  code try this :

 def _get_user_groups(self):        
        if user.has_group('group_A'):  self.has_group_A = True
        if user.has_group('group_B'):  self.has_group_B = True        
        if user.has_group('group_C'):  self.has_group_C = True

so now you make boolean fields named like your groups in your python code like this:

has_group_A = fields.Boolean(compute = _get_user_groups)
has_group_B = fields.Boolean(compute = _get_user_groups)
has_group_C = fields.Boolean(compute = _get_user_groups)

now you use those fields in your XML file by put them invisible ( to compute them each time a user go to that view),

and now put the invisible tag in each sale order to check if the user has those groups to see or not.
Note that when you make groups don't inherit previous group privilage, make every group by it's own.