Guilds are not alliances. A guild is a group who produce similar products who, through collective agreement set prices and quality and prevent non members manufacturing similar products. Therefore, why should you ever want to trade with them. However you would want to attack them if they get out of line.
HOWEVER this cannot work because attacking someone has no effect on them, and you can only attack those in your neighbourhood, and when the global market arrives they will have no impact. So, a guild, in this game, is a trading alliance. But what's the point in that as we can all produce everything?
The devs do a lot of things without thinking them through. All this "hard working" nonsense has worn thin. They seem to give no thought. The fact that there is even a hope that we should spend a sizeable amount of cash is an insult to us, the clients. They need to do a little research into market systems if they intend to develop a trading game. The city economy is fine, as I can develop very well if I want to do it in my own. Yet I know Inno have other games which have markets, which do not work. So, read a book.
All that's needed is to truly randomise deposits across the continent (if all the members have the same deposits, with 20 different products, it's not random!) or break the deposits into groups of five (say) in order of discovery and randomly select one of that group of five per person; increase production rates for good deposits (then we can have proper guilds); and use the robot traders to control cost parameters (then prices will always be realistic. Some of the young kids will understand markets even less than the devs!).
You have to have cost differentials for a market to work. Cost in here is time or diamonds. Our raw materials are houses and "production" and the usable area of city, which we use to drive our artisans or "goods". If we get the balance right, we can produce one days goods per day, and are left with no gold, no materials, and no spare population. But our advantage comes from being able to produce more goods than others, and 25% (5 instead of 4) is not enough because I can negate that by a single trade in the market place.
Infact, I've had enough of mods expecting me to congratulate a non professional attitude. I'm off to delete my city.