The mechanic should always do the alignment before removal of the old tyres , this ensures the suspension does not have to settle after being jacked up
Incorrect, ive been a tech for 12 years now and was taught never track/allign a car on old tyres.This will cause the new tyres to wear in a simular way to the old ones.Easiest thing to do is fit new tyres R/test then allign.I know not all places do it this way but every one ive worked at have done it this way,(one was a TVR
dealership).