Had to re-work a s.s. post for a local car wash. It held the money box for the vacuum station so was not in the wash itself. The stand was a bent channel and where the dies hit, it rusted the whole length. Would passivation had prevented that from happening. If someone had a small job shop I could see the price of stainless dies being prohibitive. My main question is, are there inserts for dies or what do other shops do when a small job comes their way.
several ways. we've used really thin 20-28 gauge shim stock as a buffer between dies. You can also go back and grind, pickle or sand blast. Passivation is sort of a local pickle. that depletes all the iron and leaves a chromium layer. It could work but I'm not sure how well it would do for taking off smeared steel. grinding or using shims would be my best bet. Pickling works really well, but most folks don't have pickle tank setups.
We used to use a thin durable plastic sheet, you can also walk up to it and use some pickling paste. Give it 20 min and spray it off that will take the rust and clean the stainless. You can get a bottle at McMaster Carr
I second the plastic sheet. In the industry I work we use plastic in place of stainless shims and I keep the drop pieces .020 and less for bending Aluminum tube and it works awesome!