I found a potion vendor Woot! and I stacked all the potions, even from the top row, in like stacks.
Then I went to purchase, and noticed it was buying the potions not 1 at a time, but in batches of 2-3 at a time (if not more), and the vendor's # went down 1 at a time, but I think my inventory went up 2-3 at a time and who knows how much money was being taken out.... maybe a glitch? I started with 7sp, so I think the right amount of cash for the number of potions I was getting was coming out of my purse -- but clicking should only buy 1 potion at a time. I could have had more self-control