If I put a certain amount of items to sell, lets say I put up 433 of any kind of rune for example, to sell those, would someone have to be looking for exactly 433 of those runes? or would it sell a portion to whoever wanted them?

In portions I beleive.

portions

They can buy as many of those as they want. But you'd be more likely to sell them all at once. :)

If there are unfilled buy orders at higher than your selling price, you will fill (or part-fill) those orders immediately at the buying price.

 

 

 

If there are not enough waiting buy orders, then your sell order will be competing on best price / first come terms with other sell orders.

 

 

 

There is no way to enforce complete trades.

 

 

 

For some items, it may be worth trying old-style market trading before putting them on the exchange.