She does not send the payment to Bob directly, but rather into a temporary holding wallet on the BarterDEX exchange
i. Only Bob has access to this wallet, via the set of privkeys that only he owns.
ii. However, the BarterDEX code does not yet allow Bob to unlock this temporary holding wallet; he must continue his end of the bargain first.
iii. The <alicepayment> will remain in Bob’s temporary holding wallet for a limited amount of time, giving him the opportunity to proceed.

Depends on the context of trustless .  The BarterDEX protocol itself is trustless in the sense there is no middleman between traders such as a central exchange or central blockchain.  However it is possible for a side to back out of a trade.  They are greatly discouraged from doing so through deposit,  which is awarded to the injured party when in the rare circumstance a trade would go awry.

It would be a Pyrrhic victory for the backing out party.  Yes they could thwart your trade, but it would cost them well beyond any gain they would have and you would come out with even more coin.

This is just my understanding of the system.

Shhh.. I still need to get some more KMD. Please dont skyrocket yet. 

no need to shill...
who are you anyways lol, prob one of the segwet lurkers following me around  

when a coin is doing cool stuff like,
barterdex, BCH atomic swaps....komodo will earn its value  

KMD looks prime for big gains... How big could they be?
This is my conservative estimate.   

https://www.tradingview.com/chart/KMDBTC/HtPnsGHt-KMD-looks-ready-for-big-gains/