This always leaves you the option should somebody hit you up via PM for a sampler to send it with or without something coming back to you. That something could always be another item if they don't happen to have a juice you would like to try or one you know you already like, it could be a few blank cartomizers, a couple of new/empty 5 ml bottles/ a new unused Drip Tip...something.
The Juice Swap thread is primarily for full or almost full bottles of juice. It's evident by the vast amount of 28 ml or 29 ml bottles that these are folks that could have benefited from simply sampling a flavor before buying a full bottle. If the Sampler Swap is effective it should actually lower the number of posts in the Juice Swap.
One other thing to note about the Juice Swap is the fact it can be limiting by trading 1 flavor for 1 flavor. Your 28 mls of Java Mint could have been traded in the Sampler Swap for 8 other sampler flavors, 3 cartos and 5 5ml bottles of other flavors. In essence this makes a bottle of juice you may not have enjoyed into a very useful bottle to try out a variety of other flavors.