Much depends on quality - quality of finish, thickness of plating (usually gold for altar items), and, for plated items, the type and quality of the base metal which has then been plated. Items which might look the same in a picture in an online catalog can vary considerably in quality.
One church where I live recently bought several oil lamps to hang on the iconostasis. They were not expensive, the gold plating was good, but the assembly and level of metal finishing (removal of burrs and other imperfections) was terrible. None of them hang properly, and one of the colored glasses into which the oil is poured was found to be cracked when it came out of the box. Their quality control standards did not impress me at all. If it was up to me, I would have sent the lot back, and demanded a refund.
The same church also bought two more oil lamps, from a different supplier. Again, one was not expensive. But it was made of very thin metal, and either brass or brass-plated. The colored jewels on the bowl of the lamp were not crystal or glass, but plastic. And there were visible finger marks on the "wings" on which the chains are linked. Before long, this lamp will darken into an ugly tarnished brown. This lamp either needs to be gold-plated, or carefully polished again, and then dipped in metal lacquer to protect it from further tarnishing.