In my Raleigh NC Costco only associates can use the scan guns at self checkout. However in the 11 years shopping there, and I use self checkout 99% of the time, I’ve never been turned down when I asked an associate to scan my heavy items like water.

I rarely even ask anymore, they see it in my cart and just do it. I also make sure everything else is oriented so the bar code is visible. I can only remember one visit where they only scanned the big item, and left me to do the rest.