If they're new bottles, a spritz of sanitizer before filling should be adequate. If the considerate people who return bottles give them a nice rinse or two after pouring, they should be clean enough to treat as new. If they return them dirty, recycle them - you've still got 6,999 more on the shelf.
But yeah, storage would be a pain in the extremities. If the guy won't sell you a single pallet, maybe see if your workplace has a storage unit you could use. Clearly your beer offers value to your workplace at your own personal cost, so it would only be reasonable for them to spot you a place to put the bottles. Then again, maybe you're the boss or self-employed and you already know there's nowhere to put them...
But yeah, storage would be a pain in the extremities. If the guy won't sell you a single pallet, maybe see if your workplace has a storage unit you could use. Clearly your beer offers value to your workplace at your own personal cost, so it would only be reasonable for them to spot you a place to put the bottles. Then again, maybe you're the boss or self-employed and you already know there's nowhere to put them...