Coin Pop-ups are your friend
Selling goods to these pop-up mini missions (the little coins) is not unlike upgrading your residential zones. You are paying resources for an influx of cash. Unlike residential zones, selling resour...
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Also, keep an eye on the price. Some of the NPC offers are great, and give you more than the max you can sell the items for in the marketplace. Other times the price offered is below the listing price for items. You can go to your marketplace and click on an item to see what the default offer price is. if the NPC offer is below that, it doesn't make sense to sell to the NPC unless you are in a storage space crunch. The NPC's keep offering to buy chairs from me at $165 each when they sell in the marketplace at a default of $225 coins. I tell them forget it, and soon a new offer comes in.
The only exception to that for me is raw materials like wood, iron, seeds and minerals. If I have enough, or can quickly build them in the factories, I always take those offers. The $50 and $100 sales build up, so don't skip that offer for 2 seeds for $58. Just sell them and build some more.
I would guess that overall I turn down half the offers I get from NPC's, but I am also fairly active in the marketplace.
