I think the simple fact that trap components being hugely overpriced coupled with the fact that you could easily make them out of wood is bordering on exploit. If so thats probably the only exploit Ive used. Trading everything they got every time without even touching metal is pretty strong imo.
Yeah, I've personally quit selling trap components and food just because it's so brokenly overpowered in the early game. Good things to utilize while learning the system, but really makes it too easy to succeed in hostile biomes if you can just buy 200-300 units of food and booze plus a bunch of cloth and leather for 10-15 logs worth of trap components.
Not that it isn't easy enough to make a ton of trade goods, shields, and minecarts to trade, but at least the pricing vs labor and material usage feels more reasonable doing that. Mechanisms are borderline broken too, but I'll still dabble in them when I need emergency value.
Back to the original exploit: It depends on what I'm doing. Generally I don't multiply metal unless I find myself in an extremely tight spot. That said, because caravans are kinda screwy and really need to be improved so you can make better requests, I find that sometimes metal multiplication is the only really good way to get your hands on metals you can't just dig out of the ground. Even if you move all the sliders on the various things to max, right now you're lucky to pull enough material out of a caravan to outfit a single dwarf.