The ones on the picture (my 2nd set) had no rusty crusty, so i could just use a steelbrush to get rid of some dirt and mild oxidation. For the galvanisation you need to get them as smooth as possible. Every irregularity on the surface will be visible since the galvanising layer is very thin.
The former set which is now on the car, was pretty badly rusted as well. I used a dremel tool to get all the rust of, but the dremel will leave grind and scratchmarks. Once it was galvanised, you could still see where the dremeltool did it's work.
So my advice would be to dremel it if it's rusty, and get it polished smoothly, before galvanising. Maybe even bring it to a company which can de-rust and polish it for you? The smoother the better.
• Daily driver: 2012 MiTo 1.3 JTDm • Funcar: 1998 GTV 2.0 V6 TB