Edge spots are key for spotting them imo. Most the time ads only show the chip edges in cases or racked up in bj tables. After a while you’ll be able to spot the shininess of cheap plastic chips no problem. Clay have a duller shade or fade to them.
Clay are never in plastic so that’s an easy pass. I very rarely ran into quality chips in the silver cheap-o cases. There are exceptions or course but old wood cases always get looked at.
If the chips are solids then you look for injection nipples, shininess and the plastic wrap. You’d have to ask the seller to show you a pic of the chip faces if there are none. It’s hard to zoom in sometimes and catch the mold until they give you a better picture.
Then always reference the mold guide and tag it with a bookmark until you have em locked in.