I somewhat understand the two way channels used in lightning. But I fail to see how trust is avoided.
If I'm the middle node I'm perfectly fine with forwarding a payment, if I received the payment first. The initial payer can reason that he will only make the payment if all intermediate nodes have shifted the payment to the receiver. It seems like until at least one party takes the risk the payment is in some kind of Mexican standoff.
How is this avoided / cryptograpically enforced?