I am the owner of a shipping facility in Minnesota. We ship via all carriers. First of all, like us, The UPS Store does not send packages 'Space Available'. That is a postal term that is not available, ever heard of, or requestable by any sending party or is a term that can be defined on the USPS website. What is 'Space Available'? The answer should be obvious.
Secondly, any international mailing via the postal service (which all APO/FPO's must be sent), are not trackable and have no guarantees for arrival time. Regardless of how they are sent through USPS, they often can take weeks and all too often are lost. Obviously, no alternative shipping facility can offer more for a USPS service than USPS does.
Thirdly, the only method a large box size of 36X6X30 can be sent via USPS is the Global Express Guaranteed. Incidentally, 36X6X30 is the printed INSIDE dimensions of a standard industry shipping box - outside dimensions are 37X7X31. That size is too large for ANY USPS service and would have to be cut down to 37X7X28, which makes it mailable for the Global Express Guaranteed service ONLY. That rate is $378.45. Sounds like you got a bargain! It is possible that that The UPS Store and it's post office have a good relationship and that post office is extending that The UPS Store a courtesy service - unlikely, but possible.
Again, there is no such specific service as 'Space Available' and is something USPS themselves placed on the box due to its large size AFTER USPS received it. This is outside of anybody's control including The UPS Store. I believe you owe this The UPS Store an apology for what you've put them through.
Finally, and as a side note, the BBB offers no functional service to the public. The BBB is a franchised operation that gives the false illusion to the public that it carries some formal weight. Rather, it is only a self-serving business that only 'protects' businesses that pay their 'protection' money. If businesses don't wish to pay, the BBB automatically lowers 'their' grade for this business - even though they may have no complaints at all. And if the business gets only one or two complaints, legitimate, invented, resolved, or otherwise - out of thousands and thousands of customers - the BBB will lower that business grade to a C or D. But guess what, if that business then decides to pay the BBB what they want, BBB will wipe the slate clean and give that business an A regardless or complaints. So, you tell me, what's the point?? The closest analogy I can think of for the BBB is the racketeering 'protection' that organized crime offer small businesses during the depression.
You got a great deal on your shipment. The USPS dictated that the size was too big and would have to wait for space to be available. International packages change many hands outside of USPS control and may take a very long non-trackable time for delivery. So why are you being so rude to that The UPS Store?