I think you should have a look at your own process and decide if you're happy with it rather than worry first of all about the auditor. Have a process you're confident is safe and you're well on the way to building evidence to prove that to an auditor anyway.
I'm always wary for people who say they don't need a
metal detector in their process. I've had very expensive "unbreakable" machines break and only be picked up by the
metal detector. I'd also be wary of relying solely on customer complaints to see if you need one; it's good verification that you don't but it's not something that would help me sleep at night! By using it on their own, you'd effectively be using customer complaints as validation that your processes are effective. Not the right way round IMO especially as although complaint rates vary, not all customers with a problem will tell you. Also any single find of a piece of metal (even if in your heart of hearts you
know it's unlikely to be from your site) you haven't really got a leg to stand on and could be in dangerous ground legally.
How I'd go about it is I'd audit the factory. Is there anything metal missing? Any metal nuts, bolts etc? Is there anything which could fall off your machinery which could go through your sieves? Also look at equipment on the line.
Then, I'd consider renting an
x-ray machine; or, be cunning and ask for a trial (after all depending on your findings you may decide to buy one). I'm not sure it would work for your tins but certainly in your metalised film it would be able to penetrate that and check for contaminants. You could use that as validation for your process (if you find nothing) or justification for a change in process if you do.
A cheaper alternative could be to look at a throat
metal detector. Now, they're not perfect and it is better practice to detect in the packaging but I believe they have got a lot better:
http://www.foodproce...s/2009/214.html