Now that I finally have a gathering and a crafting class up to 50 I find that I've been much more involved in the Market Board economy. I'm constantly going there to buy materials and to sustain myself I'm constantly farming and selling materials. Lately I've really noticed the restriction of 20 items per retainer on my selling habits and I realized how much healthier the economy would be if that restriction were removed or substantially increased.
For instance, I might grind a material for high quality for something I want/need. I'm left with 150 of normal quality of whatever that material is. I don't have a real need for said item, so I go to sell it on the market board. Whoops! My two retainers are 18/20 at the moment, selling bigger things that I need the gil for. I don't have a need for 150 of said item, I know that not many other people do either. It's a waste of a precious selling slot to sell a manageable say 5-10 of said item which will bring in a negligible amount of gil (compared to other things I'm trying to sell). So I either stick up a stack of 99 and a stack of 51 or I just vendor/trash it. Not healthy for me or for potential buyers.
Now let's swap the situation. I'm a botanist + carpenter so I often need things made by alchemists (waxes and oils and what not). I'm just trying to make a single item, maybe for a simple task like a provision turn-in or leve-quest turn in. It takes 1 item made by another class. I hit up the market board and...the smallest stack of it i can buy is 50. So I either don't buy/craft the item I wanted or I eat the extra cost and try to resell the rest of the stack or vendor/trash it.
The fact is, people don't want to sell small amounts of easily obtainable items because of the 20 item restriction. This is especially problematic when you look at how many crafting professions there are and how many recipes are dependent on the other classes. I don't want to waste my selling slots on fish and mushrooms when I can sell spruce logs and crystal clusters. Whenever I do something simple on my DoW as well like beastman dailies and I get 1-5 of random items like imp wings, instead of breathing them into the economy I just trash them.
If I want to farm 1000 oak lumber and sell them all in neat little stacks of 5, I should be able to, and I think the economy would be much better for it.