So, what's my utmost favorite tip?
Buying the fullest bottle.
If you can see where the liquid is, you can look at all the other bottles and compare the height of the liquid inside. I do this with everything: vinegar, dishwashing detergent, soft drinks, syrups. If you can see in it, I do it! I don't care if it's only a couple of ounces, your price is based on weight anyway so .. why not get a few more ounces for your money? It only takes a few seconds to glance at the other bottles while you've got your head in there ready to grab your item. It's a guilty pleasure but, a pleasure all the same in my mind.
I'm now into the habit of weighing already bagged produce to find the heaviest one. Sometimes one bag of onions weighs a little bit less than another so, I want the heaviest to get my $$'s worth.
It's the little things, you know ..