book stores are idiots if they think trades are better. bigger books take up more shelf space, means fewer copies, means fewer sales. even if they do charge more for a TPB. someone could go in looking for Treason and intend to buy something else and not find Treason, then decide buggerit and buy nothing.
Having worked in retail management for most of my adult life, I have some insight on this.
There are two metrics that almost any retail business looks at.
Dollars per hour. Dollars per transaction.
Bookstores like trades over mass-markets because selling a trade is going to mean better stats on both of these. A hardcover is almost never
an impulse buy. A mass-market is often an impulse buy. A trade falls somewhere in between.
Yes, some people who would buy a mass-market won't buy the trade. That's basic economics. There's a point where a certain percentage of buyers drop out of the market. So, yes, trades will see lower sales. However, the profit on a trade is higher than the profit on a mass-market. So a publisher can take lower sales, yet make more money on the trade.
Bookstores also know that trades sell less than mass-markets. But because of the higher profit margin, they can sell less, maintain (or increase) their profit, and
maintain better numbers on the dollars-per-hour and dollars-per-transaction metrics.