Professional Cleaning ???

The difference is the professional has more chemicals at his disposal and knows which type of a chemical to use and how to use it in each situation.

EDTA (Ethylenediaminetetra-acetic acid) is best obtained as a disodium salt. Even then it should not be inhaled.
BTA (Benzotriazole) is a great corrosion inhibiter but also thought to be a carcinogen.
Acetone must not be inhaled or ingested, same with zinc powder.
So most of the things that work best are terrible for your health and though might seem to do a great job of cleaning, an item may well need another chemical to neutralise the long term effects of the first.

I saw a demonstration about ten years ago where silver items would be put in a glass jar then a gas would be introduced. This re converted the 'tarnish' on the silver back to silver. So you could have a plated silver teapot and clean it without ever polishing through to the base metal underneath.

You could study conservation and be able to do it as well as the professional in most cases if you could gain access to the chemicals he is allowed to use. I completed a conservation course but either can't get hold of some chemicals or would have to buy a gallon at a time which would last years and is fantastically expensive.