I just spotted a Silver Potion restocking in the shop and went for it... only to find that it was priced at 0sP. I went to buy it anyway, just to see what would happen, but 100sP was too much and by the time I put in 1sP someone else had brought it. I don't know the official price but I doubt it was less than 100sP; the fact that I could have, and that somebody else probably did, buy it at less than that seems like a massive glitch.

I saw this too! I made a ticket about it as well.

Thanks Amber!