Brokerage and when to execute

[nick123]

In CFAI BOOK6 P60 Question9
Assuming brokerage and we sell a stock representing a customer. The order is sell, prices have been increasing since the open. Broker should immediately fill the order. Why? I thought selling later is better as it is upward trendong
Can somebody explain?

 

[MrSmart]

Higher volume and lower slippage costs?
If it’s a sell order, the broker shouldn’t have a say on when to sell all else equal.

 

[nick123]

Yes this is for sell order case and would be opposite in case buying according to CFAI EOC Answer. Im not convinced yet though