How to make Settlers of Catan less cut-throat?
3:1 trades are not unfair; they're bank rate. At which point the trading partner should simply trade with the bank, as that is a winning strategy. Anything better than 2:1 is better than dedicated port trades, and is only useful when you will gain more than your trade partner.

My recommendations for curing both at once are straightforward, but brutal. And they are not exactly "Tournament Catan"...


restrict the nature of offers.
one pass only on a given resource offer.
reply in sequence only.
no "counter offers"
No rejection of particular opponent. 


By restrict nature of offers, limit it to offers of "I have 2 X and am looking for a Y". I'd allow the following rates: 1:1, 2:1 &amp; 3:2. (3:1 should be restricted to bank trades via a port only.) Likewise, if you have the resource port, you should be required to use it instead of making a 2:1 trade offer.

One pass only means, if no one bites on the offer, you can't try it again that turn. If it is accepted, it can be repeated.

Reply in sequence only: if players are (in order) A, B, C, &amp;  D, and it's A's turn, he makes the offer, and B either accepts and holds out the asked for resource, or B rejects with a "No." then C gets the same option. If C rejects, D gets the offer. If D rejects, it's dead. Offer something else or yield the turn.

No "counter offers" - either they accept or reject the offer at hand. No discussion, no "how many will you trade?" It really speeds up play to disallow counter-offers, as it eliminates the whole negotiation mindset and the attendent waste of time for others.

No rejection of players: by eliminating trade preference, one forces trade to be quick and about getting what you need. This one should not be a permanent solution - half the strategy in real play is avoiding trade with the leader.

I've played with these restrictions in force. It REALLY speeds play, and reduces the ability to play favorites. I did so with a group of 6th graders, and ones with strong issues with each other at that. The No Rejection was a means of overcoming a couple of players racial biases... but it also changes the nature of play, hence later changing it to "once you make an offer, you may only refuse to trade with someone if they have more VP than you."