1-you need to use a chemical testing kit, you can't tell if it's legit from tasting it. The "taste" is usually cutting agents anyway
2-they bring their own, but really the main thing is to find one that you can actually leave there the night before to watch. Cops rarely set up before the shift starts, but finding someone who has two brain cells to rub together and will actually watch instead of wandering off or falling asleep is the hard part. it's smarter to pepper spray them than to use guns if you are stealing anyways-not a huge deal to get caught with pepper spray and some pepper sprayed guys claiming their drugs/drug money was stolen-what are they going to do, go to the cops? shoot someone and they won't ever stop looking for you.
At least that's what my mom says, I'm a librarian.