Principal vs Agency 
Principal Bid: A transaction where a broker/dealer provide an investor with guaranteed execution of the trade list at the market prices at a specific point in time. All timing risk is transferred to broker/dealers. Investors are charged a premium for this.
Blind bid: investor provides only trade list statistics. Than broker/dealer defines the price.
| Trading Cost | Agency Exec | Principal Bid Transaction | 
| Commisson | Y | N | 
| Price Appreciation | Y | N | 
| Market Impact | Y | N | 
| Timing Risk | Y | N | 
| Opportunity Cost | Y | N | 
| Premium Fee | N | Y | 
| Known Price | N | Y | 
| Granteed Fill | N | Y | 
| Forecastablility | Distribution of cost | Single value estimate |