Cdel is retail, they are one of the largest. Almost all my brokers will route orders through them. I try to avoid them when possible. They have a trading division. If a MM is trading on the same side as an order they take, by law, they are supposed to fill the customer order first. Not only does cdel break this rule almost always, they use customer order against the customer in favor of cdel. Good luck proving it. But I have found hints that let me know. If you put an order on l2 and cdel takes the order and puts your share request on say the bid, then cancel the order, if they stay as high bidder, but the shares drop to 1000, then they were going to keep your shares. If you put an order for 10k, and the order shows 11.5k, they are going to fill themselves first. I have actually seen my order being hit on l2, then cdel drop off, meaning they 100% got those shares, just to see my order pop back up without me getting any.

http://finra.complinet.com/en/display/display...nt_id=9989

5320. Prohibition Against Trading Ahead of Customer Orders
(a) Except as provided herein, a member that accepts and holds an order in an equity security from its own customer or a customer of another broker-dealer without immediately executing the order is prohibited from trading that security on the same side of the market for its own account at a price that would satisfy the customer order, unless it immediately thereafter executes the customer order up to the size and at the same or better price at which it traded for its own account.
(b) A member must have a written methodology in place governing the execution and priority of all pending orders that is consistent with the requirements of this Rule and Rule 5310. A member also must ensure that this methodology is consistently applied.