I'm a bit sceptical about this. If it comes with an option to enable or disable offers then I think I'm all for it. Could be great if you had the ability to partially fulfil offers with gil-alternatives too. For example, someone selling HQ Electrum Rings may be interested in taking part of the cost in something like HQ Electrum Ore or a large bulk of Wind Shards. With the ability for the seller to view these items market values before accepting of course.

In addition to this perhaps give the retainer the ability to post a message with their sale such as "CPW (can pay with) Wind Shards: 1 = 100 gil". Might be too much of a server burden to have a different message for every sale, but if you had one message per retainer for all of that retainers sales, that could work.

It's just a personal thing how I like that my prices aren't up for debate. The advantage of posting under retainer names is that nobody can harass me through PM over the prices I've set. There are only a few things worse than being haggled by someone that won't listen when you tell them the price won't change. Or having a competing seller trying to tell you how to sell.