I was a scout leader at the time, and one of the other leaders phoned another scout group to rent their building for our summer camp. They mentioned a price, he said "okay", intending to be "okay, I understood that's the price, let's discus" whereas they took it as "okay, I agree to this price, and we'll rent it".

Long story short, turns out verbal contracts like this very much are enforcible, and they were pretty adamant about enforcing it. Who knows if it would have held up in court, but just paying the "cancellation fee" was cheaper than lawyers,

Absolutely outrageous a volunteer non-profit organisation would squeeze another volunteer non-profit like this by the way; this was well before the planned date and the confusion came to light within days of the "okay", so they suffered basically zero damages. Bunch of twats.