There are two main types of items: high volume low margin, low volume high margin. Most crafters prefer the high margin items. The problem is, some people have all day to lower prices by 1 gil back and forth. Those people will make your life miserable if you don't have the same amount of time to watch the mb all day. This could be avoided by adding a 1% tax your retainer charges to the asking amount when you list/change prices. If you are selling a 3 million item, and it costs you 30k to lower the price by 1 gil you will be less inclined to spend all day undercutting each other by 1 gil.