When I was kitting out my FDL I had to spend an hour buying items, launching, flying outside the firezone, trying them out, swapping them for something else, changing shield boosters, up and downsizing scanners etc just to get a load out that would work properly because of the lack of power. I must have made about 15 changes in total.
The 10% module fee without any extra thought for returns and or storage is just taking away from the gameplay, and making the game worse not better.
You could live with ships requiring a lot of thought on load out, but loosing 10% just for trying out a weapon for an hour or so is no good at all. I get 28 days on most products at home, this 10% immediate loss for returning a product would make this game less enjoyable especially on multirole and ships requiring a lot of thought on the loadout.