Neither did I till I showed him all the bits I needed to get done, I'm playing around/restoring a Genuine E30 318is at the moment (I should really start a thread at some point) and didn't want to muck around with the factory ride height too much.
PowderPros use Prismatic powders and they were quite confident about the durability and that there would be no damage to the original spring, I did do a little bit of research on there website: https://www.prismaticpowders.com/gallery?htids=Suspension
@Vass They really take the each job on a case by case basis and to be honest my arms weren't really in the sharpest condition to begin with (surface rust) , James at PowderPros did mention to me with these sort of jobs its best customers drop everything off at once as staggering the parts can add some time and cost to the overall job, I would highly recommend you have a chat to him if your interested.
@Neil McCauley the process for all the parts: Acid Stripped, Sand Blasted, Zinc Primer, then colour: Gloss Black or Silver then Clear