I reside deep in the Hill Country of The Republic of Texas.
Texas, unlike your lovely home state of California, has no statutory provision for a citizens arrest.
All states allow a merchant the ability to inquire of a person the merchant's personnel believe to be in possession of purloined goods.
In the scenario you posit, it isn't governed by law, it's driven by a picture is worth a thousand words.
Thank you for the serious and thoughtful response to my inquiry. It appears that the majority of posters disagree with me and are all too happy to abrogate their God-given and Constitutionally protected rights in the name of loss prevention!
Best Buy, Ross, Target and a few others station a human clothed in store protection paraphernalia to greet you as you enter the store. Psychologists believe a friendly greet will deter the average Jane and Jack from engaging in theft.
The scan your receipt as you exit SAMs Club, BJs Warehouse, COSTCO, and others is to put the thief on notice, Poppa Protection is watching you.
In Texas, it's meaningless, a toothless charade, naughty kabuki dance, or for appearances. I have discussed the intrusive, insulting nature of such practices with the general managers of those stores in my area.
Each manager that I spoke to about the practice apologized profusely after hearing my side of the story. For some odd reason, it could have been the lawsuit I filed against the largest SAMs in the area, and having about 150 subpoenas served on store employees, managers, regional execs, and all of the videotape I sought during discovery.
These days we're all on speaking terms, and I hold no grudges for my refusal to show my receipt to the greeter. You see, she pushed a cart into me, as I drew back when she wanted to snooping my bags, filled with legitimate purchases.
The police were called, and it could have been when the patrol sergeant said, "Howdy, Judge!" Or, it might have been whence told the duty manager that Texas, unlike some states has no citizen arrest statute. Only a manager, certain designated store security personnel that had been surveilling a suspected bad actor, could under those narrow circumstances ask to see a receipt. Of course, if the suspect refused, the issue of detaining such a person is fraught with great legal risks. I'm sorry, I digressed. LOL
In Texas, customers don't have to submit to such searches, generally.
The legal issue is probable cause versus mere suspicion, and coercion versus cooperation.
People do have the right to say no to law enforcement personnel.
Absent certain exigencies, law enforcement would then need to obtain a warrant, or use guide and tricks ration to solicit consent. LOL
In the other members of our rather fragile union, blue versus red, the answers vary.
By the way, the big box chain and I settled our differences by sending me a letter of apology, and $100 gift certificate, which I gave to one of our local homeless shelters.
Thanks for asking such a great question.
Some of our other regulars will certainly chime in and offer their unique, diverse opinions for you to chew on, mate.
Between us chickens, boss, my wife pushes the cart out of the store these days.
She enjoys the small talk as the store employee draws the colored line across the receipt. LOL
Here are a few good articles that discuss your question:
Loss Prevention, Retail Store Exit Bag Checks, security consultant, Chris McGoey, retail loss prevention expert
http://lifehacker.com/5853355/know-your-rights-if-a-store-detains-you-for-shoplifting
Are Receipt Checks at Stores Worth the Hassle? - Lawyers.com