Ummm... not in THIS state - they have to see you select an item from within the store and conceal it. Then, and only then, could they detain you. At that point, if you refuse to turn the item over, they would be forced to call the police and THEY would perform the search...
Well, basically that would be the way it would happen in your house too (you'd detain and call the police). I don't want to really get into gymnastics over the comparison because that wasn't what I was getting at. The good strong reason in the store's case would be them seeing you take the item.
The poster I responded to had the scenario of selling a chest in his home, leaving the room, coming back and noticing that other items were gone (presumedly stashed in the chest). My point had been (which I probably didn't make clear enough) that then you would have a reason to act, just as the store would if they had a strong reason to suspect you took an item (ie- the store detective saw you). But if you had sold the chest in your home, made out the receipt in front of your buyer and took his money- what reason then would you legally have to detain? None, in my book. This is where the analogy was somewhat flawed, because in a store nobody's going to look at any given shelf and say "hmmm- one of the Barbie Dolls is missing" and immediately think one particular person must be responsible.
But bottom line, if the store has no hard reason to suspect you in theft, they also cannot detain you.