I thought the principle of liquidated damages was that they were supposed to be a reasonable estimate of hard-to-calculate damages, and if they were just a dete

I thought the principle of liquidated damages was that they were supposed to be a reasonable estimate of hard-to-calculate damages, and if they were just a deterrent, the other side could argue that it was an unenforceable penalty. The reason I was researching this is because Stubhub's support website actually describe their liquidated failure to complete transaction damages as a "penalty," which seems to be a major mistake on their part.