Items sell for 75% of their original value, rounding to the nearest ten.
You can carry a maximum of 19 - any picked up after that will require you to discard one.
Secret shop[edit]
In addition to the normal shops that appear at the beginning of every level, there is also a 'secret shop' that allows you to buy many rare and useful items.
To access it, when you are on the screen where you can hire troops, equip items etc., press 
. You should hear a special sound to indicate your success. Now, go to the shop menu. The shop for the current scenario will have been replaced with a new one.
Ultimate secret shop[edit]
There is also an "ultimate secret shop" which you can buy all items shown in the game.
To access it, when you are on the screen where you can hire troops, equip items etc., press . You should hear a special sound (bombing) to indicate your success. Now, go to the shop menu. The shop for the current scenario will have been replaced with a new one.