Premise #1: Crown sinks (in moderation) are good and useful things to have, particularly if they are not the sort of thing that upsets people much.
Premise #2: The current state of affairs, where a small number of wealthy individuals can seriously manipulate the prices in the energy markets without real cost to themselves by herding other buyers/sellers with offer walls is regrettable, and low-cost solutions to this would be worthwhile

Given these two premises, I would suggest two changes.

- First, change the 2% crown fee so that it functions like the AH - applying at time of offer, rather than time of sale, and is paid by the offerer, whether it's a crown-for-CE offer or a CE-for-crowns offer. This will mean that there is a real cost associated with attempting to manipulate the markets via offer walls - particularly offer walls that the offerer doesn't ever particularly want to see breached. Keeping the fee down at 2% should keep it from being a huge issue for the people who are actually interested in buying and selling CE. It does mean that accepting offers becomes more appealing than making them to a degree - if your offer is not accepted and the market moves past you, you're effectively out the money - but that might not be such a bad thing anyway, and it opens up a bit of (somewhat risky) space for people who want to play the market from the middle with relatively small numbers of offers without pushing it one way or the other. Of course, it would result in an additional crown sink - it effectively adds a 2% crown cost to canceling an order.

- Second, limit the number of offers than a single person can make to 10 or so at a time. It needs to be more than 8, so that you can make enough offers to craft a single 5* piece of gear at a time, but it would make it significantly less trivial for wealthy individuals to throw around the 100-strong offer walls that effectively force smaller buyers to move ahead of them. It would make market movement far more about a number of people working in smaller bits. Of course, if you really wanted to drive the market, you could *accept* as many offers as you like - but that's spending real money.

Either works alone. The limit without the fee means that offer walls are a lot less trivial to set up and move, but mostly that will mean that it's something that gets done by groups and guilds, rather than individuals. Individuals will still be able to manipulate by accepting offers, which will provide a bit more of a crown sink, but I don't suspect it will be all that likely to be a major one. On the flip side, fee without limit will mean that at least the people who want to manipulate the markets will have to pay for the offer walls they set up - that'll provide at least some limitation to them, and also a fair amount of discouragement.