If brokers will never present lower offers to sellers, they ARE artificially keeping prices higher than sellers may be willing to sell at, however, and then catering the market only to those willing to pay the higher price. If brokers weren't preventing lower prices from going to sellers, there's a good chance the average selling price might be a little lower than what we are seeing now.
I had one broker at
www.dvcresalemarket.com refuse to send an offer to a buyer because they would want to buy it themselves at that price (and I imagine turn around and sell it for a higher price). They also told me that the price was too low and that no seller would accept it. Except that I literally had purchased a contract for that exact price on a fully loaded contract only a month before.
Brokers don't control the market, but I think you are undervaluing the influence they have in ensuring low price offers that a buyer might be willing to accept never make it to the buyer, and thus they do have influence in keeping prices higher than the market might actually bear.
I have purchased 11 resale contracts over time, and only 4 of them did I ever pay the actual asking price. But I think that's why I value brokers at
www.fidelityresales.com,
www.*************.com, and
www.DVCbyResale.com who have all been willing to work with me and presented my offers to the buyers, allowing US to negotiate on what is a fair price.