Just watched a real-time speedrun of Monopoly on the NES. Basically, the player exposes how idiotic the AI is as he mortgages off all of his properties, offers them ALL to his opponent for his properties and all of his money, then the AI goes bankrupt because he can't un-mortgage or even pay the 10% principle to receive the properties. If you play the SNES or Genesis versions however, if a trade makes it possible for this to happen, it will say that the player will not have enough money to receive the property, forcing you to decline the trade. Gave me a good laugh.
Basically the root of the NES Monopoly's AI is that they value railroads and monopolies VERY highly, even to the point they'll accept the Mediterranean/Baltic monopoly even if it gives you 2 of a far superior color. And if YOU get a monopoly out of the trade, good freaking luck getting the computer to accept your trade. Well to be fair, the Genesis version's AI isn't any better, although they have an obsession for gunning down trade offers, yet will happily take the Purple Monopoly in exchange for giving you the Green Monopoly. Keep in mind the Purples (Browns in modern versions of the game) are all but junk. If you get it early and are playing against 4+ people, it could benefit you, but other than that, those two properties are garbage.