If you're smart you would have a on-line account so you can log in and see what the order status is.
I've ordered stuff over the past two years and never had a problem. I go into this knowing that items like uppers and lowers are built as they are ordered and may take a few weeks to ship even if they show "in stock". I have never had my credit card charged until the item ships. If you need it today go the the LGS and pay twice as much. It is well known PSA ships on the slow side, if you are in a hurry, go elsewhere. If you want to save some $$$ then it's the right place.
As far as receiving the wrong item, PSA does not have a monopoly on that. I have gotten the wrong item from Midway, Brownells and others.