I'm a big fan of the Costco business model and have been a member, based originally at Bushey in the late 90s before frequenting the Chingford warehouse for a spell till the Stevenage branch opened.But respect to Costco for installing them, and making them free.
I try to gauge my fuel usage in such a way that I can link a Costco shopping trip when my tank is down to a quarter-full or less to take advantage of Costco's diesel which is almost always significantly cheaper than anywhere else in those parts. If I leave refuelling till the tank is almost empty, I can get something of the order of 73 litres in the 70 litre tank if I brim it. Given that the fuel stations near to my neck of the woods are usually about 10p per litre dearer than Costco for regular diesel, deciding where to refuel doesn't require a degree in maths! 😁
While there are cheaper places to shop for various items stocked by Costco, there can be no doubt about the level of quality, whether it be fruit & veg, butcher meat, fish, clothes or whatever. Their tyre department does great prices on Michelin tyres and their batteries are competitively priced too. From time to time, they have special prices on a variety of products and I have snapped up a few bargains over the years. I'm not a lover of pizzas but I can say that those baked one the premises are excellent and very well-priced. While I can buy meat cheaper elsewhere, I really don't mind paying a little extra for Costco's product as it really is worth the extra.
Costco have been doing a car-purchase scheme in conjunction with a few car brands that looks like a fairly attractive proposition at first glance. I haven't researched it as I'm not in the market for a change yet but I imagine the deals will be competitive if not mind-blowing. They had a Toyota Highlander on display last time I was there and that makes the RAV4 look like a compact!.....not cheap though! When I'm back in the UK, I might look more closely at the Costco car purchase scheme in case I'm missing anything there.