but i cant buy that iron shield
Now, pick up the equipment you bought. If you traded for money, stacks of money should have appeared, and any items you traded for lose the $$ tags around them. Any item with a $ tag will count as stealing if you take it, anything you traded for should not have that tag, and is safe to take. Same for the cash.
It confused me quite a bit too at first. All the items are just sitting around on tables in the shop, you need to grab them yourself after purchase.