I only knock the stores and fuel stations that deserve it. You are not the one delivering the fuel so how would you know? High marks from consumers mean nothing to the guy who cleans out a throttle body, throws codes for having too much ethanol in the fuel, or has injector damage.
The average motoring public has no idea what they are pumping into their tank. Cross dumps with 87 into the 91 and level 1 diesel into gas are a common occurrence (and not just Costco) for high volume stations. Reason being the drivers are very rushed to get in and out. Arco is an example of many.
After delivering fuel for almost 20 years I have learned that Chevron and Shell are the only brands I trust in my vehicles. Of course a tank of something else every now and then won't hurt. Their guidelines and regulations are the strictest in the country.
Just for general info Chevron does not allow diesel and gas on the same truck. It has to be drained dry of gas before diesel is loaded in the tank. I say this only because I know how strict Chevron is about keeping fuel separated and preventing "a hot load" of diesel. One small quart of gas in a 1000 gallon compartment of diesel is considered contaminated fuel.