Right now, at least on the iPad version, when you’re accelerating building timers using 12 hour speed boosts, you need to confirm each boost by clicking an accept button.
Of course, that accept button is RIGHT OVER the button to spend gems to finish the construction. On multiple occasions, I was trying to accelerate a building by several days using multiple 12 hour boosts, and then accidentally clicked the button to use gems. Of course the gems button DOESN’T have any confirmation - it just immediately deducts gems. I’ve probably wasted over 10k gems accidentally hitting the gem button, including 4k on a single building today.
If I was the cynical type, I’d say Pocket Gems purposefully designed the interface that way, to get players to waste gems and have to buy more.
I tried contacting customer support, but they said they can’t refund the gems, due to concerns about fraud. They suggested posting here. Hopefully this will get some traction and a fix - the button to use gems really needs its own confirmation box, at least for anything over 1 hour / 60 gems or so.