OK, start the groaning now because "inventory" has to be one of the most dreaded words around. No one likes to crawl about to find and count the myriad parts that are on trucks, in stockrooms, garages, shelves, desks or wherever else you keep your parts.
But answer this: Do you have any idea of how much money you have sitting there? Maybe about tax time when you HAVE to account for your parts but how many times do you want to do that? How many times have you ordered a part because "I know it's here somewhere, I just can't find it!"
Now, I am the last one to preach about organization (at the best of times my desk looks like a hurricane hit it), but when parts are your bread and butter, it pays to keep track. It may take awhile to get your truck, stockroom, garage, whatever, into shape and to inventory those parts and train yourself to keep up on it (kinda like cleaning the gutters on your house and just about as fun). But when you realize the amount of time and money that this will save you, it will be worth it.
There is lots of software out there for you techno people (you probably have it on something you're using now but haven't utilized it) and it can integrate it into your invoicing and definitely make tax time a lesser burden. Also, lots of storage containers for those parts are out there!
And those parts that you have no idea where you got them and haven't used and have no idea what they go to? Try networking on the internet to get them to people who are looking for them. There are lots of "antique" appliances out there people don't want to get rid of and parts are no longer available for them but they will hunt to the ends of the earth to find them to keep their beloved appliances.
Send me a postcard from your vacation with all the money you've "saved"!
Have a great week!