I think I found (one) place where I got the idea that selling map info to the AI could encourage them to attack. This is from a guide to Gaul in the Scriptorium:
http://www.twcenter.net/forums/showt...94#post1004994
The relevant part:
"You may be tempted to sell map info to your next door neighbors. Don’t! They will attack you the very next turn, since you have stripped down your defenses to attack the starting rebel cities, and selling map info shows this to them. In general, only sell map info to factions that do not share a border with you."
This seems to have been written quite some time ago. I guess the theory is that either the AI can "see" your lands without fog-of-war once you sell map info (I don't think this is the case), or that the AI can do the equivalent of "double-clicking" on an enemy city that is concealed by fog-of-war to determine how many units are garrisoned there. Either way, it doesn't seem too convincing; it could simply be coincidence that the AI attacks after a map info deal, since there can be many factors involved in determining when the AI attacks.
I guess the only way to test would be to see how the game plays when you don't sell map info, and then see how it plays when you do. I've avoided selling my map info for years, so I'm actually in a decent position to test out what happens when I start selling it. But again, I'm not confident it's going to be a big difference.
(As an aside there's also this bit about trade: "You can sell trade rights to the surrounding factions for about 1000 to Julii and Germania, 2500 to the Carthaginians, 3000 to the Britons, and sometimes 5000 to the Spanish. But, to get this high a figure, you need to have roads, ports, and traders established, because the AI figures the worth of the trade agreement based on trade income, and roads etc make trade possible.")