That might be true for clothes or food, but even that is dubious, more likely some old wives tale that represented a nugget of truth long ago that has been passed along as a marketing story. Having worked at BB in the past with access to the store cost on many items, I can tell you with 1000% certainty Costco's margins on stuff like electronics and small/major appliances are nowhere close to 15%, even diluting it with comically ridiculous amounts of overhead and cost of business expenses. For starters 95% of name brand stuff is price controlled these days and they literally wouldn't be allowed to sell it 15% over invoice even if they wanted to, the major manufacturers would collude and pull their entire allotment by the end of a business day. Protip, the $3000 77" OLED at Costco that's simultaniously $2000 on Greentoe is still being sold for a handsome profit even at $2000.
I work in the industry. You can even google it yourself as it’s common knowledge. Costco is not selling a $3000 tv at a dirt cheap cost price.
Unless things changed a lot the past 15 years, I used to work at an electronics company too. The reason why electronics stores sell for cheap is because they get monthly or quarterly discounts from the supplier to flush out inventory so the prices of electronics swing wildly so Future Shop or Best Buy Canada back in the day aren’t stuck with something at a high cost all year.
Even for small stuff like food, even if they can make higher margins they don’t. They will literally ask for a higher invoice price so the margin maxes at 15% at the agreed to retail price. Or if the retail price suggested by the acct manager makes sense, Costco will just say set a price that makes it 15%. So we literally just make up an invoice price afterwards in a weird reverse cost way.
For small electrics it’s still 15% (give or take as the lowest I’ve seen is 12%). My current company sells small electrical gadgets too and it’s the same method as food and cleaning supplies.
Pending how systems are set up, the invoice cost you see is probably just that. Invoice cost. You wouldnt see all the back end discounts given since those are rebates back to the store after unless your systems showed everything. Your system probably wouldn’t show other discounts a store gets from suppliers like terms and refund allowances either which aren’t part of retail margin math.