Eric is on the money. Prep is what it takes. If the parts are oily or rusty and you send them in that way, expect the same unless there is communication to what they are going to do. I had a local shop that would work with me on pitted or badly rusted chrome, even pot metal parts. I would clean and sand/grind them smooth and even drill out pits. The shop would plate them in copper so silver solder could be used to fill in the deep pits. Then I would send them back and they would plate it with nickel, chrome and then polish. The results were much better and cost was very reasonable.
If the shop has to do it then plan on higher costs.
Bill