In trading exchanges, there are buy orders which offer very far lower prices than the market prices.
Are these orders trustworthy? Will we get the coins we order?
On centralized exchanges, orders are executed immediately after you redeemed them. Therefore, if someone made a mistake and placed a very cheap order, then you can redeem it.
Some decentralized exchanges fail and there may be an order in the orders that someone bought earlier, so you need to check them before placing your order yourself.