There's always going to be constraint. If you want to compare with Walmart, they have way more possible items to sell that the game does, not to mention hundreds of other factors that will determine what and how many ends up in which shelves. What I'm saying is work within the constraint...that's what all succesful trader does.

If an item is not profitable to sell in small quantities, then find something that is profitable...If there is a market for small quantities that the seller finds it worthwhile, then there will be sellers who's willing to break bulk. If no one wants to breakbulk, that means the bulk won't sell, supply will accumulate, and price will fall.