Jones replies to the question; "Not a spellcaster, but he has regular contacts whom he hires for spellcasting services. So thus why press on urgency steal the chest itself or if possible silently cast a spell to undo the arcane lock, leave the chest behind and then rush to me to avoid complications caused by divination magic cast on the tiara. If want to make it appear no heist happened, you need to forge a replica for the crown but with a given time limit it can be tough to impossible to make a convincing fake and any expense to do so would come from your own pockets. As the merchant is an expert on relics so replica needs to be seriously convincing."