RAW: Most likely not, however, it would depend on the DM.
The Divinity of the Cleric's Blessing Channel of the Clergy Forge Domain says (XGtE p. 19; emphasis mine):
You perform a one-hour ritual that creates a non magic item which must include some metal: a simple or martial weapon, an armor, ten ammunition, a set of tools or another metal object (see chapter 5, "Equipment", in the Player manual for examples of these articles). The creation is completed at the end of the hour, merging into an unoccupied space of your choice on a surface less than 5 feet from you.
What you think may be something that is not worth more than 100 gp. As part of this ritual, you must place metal, which can include coins, with a value equal to creation. The metal unites and inevitably becomes the creation at the end of the ritual, magically forming even non-metallic parts of the creation.
The writing of Channel Divinity seems to limit it to specific elements of the Team Chapter in the Player Manual. Plate armor has a cost of 1,500 gp, which is too expensive for the player to cast a spell.
What is not certain is if you can do multiple pieces of an article about multiple castings. Since the function does not say that you can, I suppose you cannot, strictly Rules as written. However, it would ultimately depend on the DM.
If you wanted to make it easier for players, you could:
- Allow them to cast Artisan's Blessing 15 times to make 15 pieces of plate armor, each with a value of 100 gp.
- Then, using the tools of their blacksmiths with which they are competent, they could manually forge them into a complete plate armor.
They would still be spending the same amount of gold, and it would take them 15 days to create the plate mail. Especially in Curse of Strahd, where, according to my experience, it was quite difficult to acquire specific items, most likely it is balanced to allow this.
As to how this can affect the character who wants to sell these items / weapons, one could say that nobody would want to buy them, as they would be too expensive.
If I wanted to buy a plate armor, it would cost me around 1,500 gp depending on what the DM says the NPC sells its plate armor. Now, it costs Forge Cleric 1,500 gp do this plate armor, so if they want to earn money they would have to charge more than that.
Like DM, you could say that nobody would want to buy Forge Cleric items at those much higher prices if they don't want to.
The Vistani can travel freely from Barovia, and they are merchants / merchants themselves. They could easily manufacture, exchange or buy items for cheaper prices than those that Forge Cleric would sell them.
Alternatively, one could say that no NPC would want to risk their lives by buying items from the cleric of Forge since Strahd has forbidden them to do so. These are just some of the many ways you can prevent Forge Cleric from trying to establish a store.