I definitely think that the two Nystul spells should be added to the Merchant tricks list. I was also thinking a good ability would be to allow the ability to increase with level, as in at 6th level they can cast two tricks per day, but my only cast a specific spell once per day, in effect you couldn't cast arcane mark twice in the same day. At 12th level they can cast three tricks per day, but each specific spell only once per day. At 18th level they can cast three tricks per day, but may cast a specific spell three times if they wish.
Thoughts?