Currently, when attempting to buy zero of an item on La Paz Market, the following occurs:

 

1.  a message is displayed, 'Well done. You bought zero items'
2. the listing remains but does not expand when clicked
3. when clicked again, the listing disappears. (Fixed on refresh)

 

Obviously a bit of an edge case/unlikely scenario but thought it's worth mentioning!

Further context (I just tried to reproduce and couldn't until I realised):

To reproduce:

1.  have cash on hand to buy one item (not enough to buy two)
2. buy one item
3. now, the option to buy zero is available