My question is, how do people make profit by selling in items board? I have seen that the item prices in items board is lower than market, which means we can buy for lower price in items board.

But how do people make profit by selling? prices are already lower than market and selling will lead you to loss.

Please explain how it works.

Uh it's like this:
People buy item for 10k in items board.(market price is 13k)
Then they sell it in items board for 11.5k.
it's all about haggling.
Usually newbies has the lowest prices,since they aren't so experienced in marketing.
Basicly all the selling and buiyng happens in items board,you search for the lowest price,haggle it down and sell it bit higher.(Don't forget that price should be lower than Market price,so people would be interested.)

EDIT: Prices are approximate.
/offtop if you have some items to sell,pm me.
Because i was thinking of making a shop again and we could do it together.

That's a good profit in your example. I get it now. Thanks, ;)
As for shop, I will respond via Pm.