Just like any business, there are outside physical inventory service providers who are considerably better than others. Some dealers and dealer groups will only allow an outside company to perform their physical inventory; often to obtain "certified" results to satisfy their accountants, bankers, owners, etc. If you are either required to use an outside firm or are interested in possbily using an outside firm, simply ask for references and check them out with the parts manager of dealerships they have inventoried.
You should also insist on a list of exactly what all the services the outside firm will provide. Do they use parts people as crew members, or do they count shoes one day and parts the next? A quality outside company can bring a lot of experience to the table as far as knowing where to look if there is a problem or discrepancies that many people who do their own don't realize. If nothing else, some companies will offer to come in and for a lesser fee help you and your people administer the physical inventory. An independent set of eyes can often see things that you might miss that kind of "blend into the scenery". An independent can also offer suggestions about how to better do things or handle certain situations based on gleaning the "best practices" out of seeing how many dealerships do things. Again, like anything in life, you get what you pay for. Just do your homework and check the references.
[This message has been edited by scotstrong (edited 10-25-2002).]