"Cleaning gold is very different to cleaning steel."
I use a double sided 'Fabulustre' cloth to remove tarnish and polish the surface if needed. It has a very mild polishing compound applied to the (red) cloth and the other side is a soft (light yellow) polishing cloth. When using polishing compound on a soft cloth (I use mostly Wenol Ultra Soft), it is a good idea to apply the compound to the polishing cloth and rub it in the cloth and not apply it directly to the watch. When you apply the paste directly to the object it can sling into spaces between bezels etc. I do not use powered buffers on solid gold, especially 18k, hand polish only. Besides removing too much material, powered polishing wheels can catch an object and send it into orbit.
A few of my friends are in the gold and diamond buying/trading/selling business and they can usually spot solid gold watches right off. I can tell sometimes but do not have an exact explanation why but it may be because solid gold has a warm, subdued appearance and plating is usually shiny and harsh.