If you were asking about how the rating points work and why they seem "random", here's the answer:
When two teams fight, the winners and losers are each awarded or penalized the same amount of rating points. For example:
Winners: +15 rating
Losers: -15 rating
In the above example, these might be two 1500-rated teams at the start (though post-game they'd be 1515 and 1485).
The rating/ladder system expects that a higher rated team should win over a lesser rated team. So the points per match are altered to reflect that. In another example, a 1600 point team plays a 1500 point team.
1600 Team Winners: +13 rating
1500 Team Losers: -13 rating
The points are less than two evenly matched teams because the 1600 team should have been slightly better than the 1500 team. However, if the 1500 team had actually beaten the 1600s (a nice upset for the underdogs!), the points allocation would have worked out something like:
1600 Team Losers: -17 rating
1500 Team Winners: +17 rating
If these same two teams fought only each other continuously, their ratings would naturally converge to some value that would be indicative of how often the other team beat the other. If they were exactly 50% win/loss against each other, both teams would hover around 1500 rating.
At the extremes, the numbers get even farther away from a +/- 15 type award. A 2000 rated team fighting a 1400 team would receive only a small handful of points if they won, and could lose 22+ points if they were beaten. The matching system doesn't often put together such teams, but it can happen.
With me so far?
What a lot of people get upset about is when they lose to a team that is experienced/geared/skilled enough to really be rated much higher than their team's current rating. You may get handily spanked by a bunch of players who are intrinsically geared and skilled enough to be 2000 rated, but are currently playing on a team with a 1400 rating. In essence, you take a bigger point penalty than you should if you had been playing a properly rated 2000 team. (You're still going to lose most of the matches to them, it will just depress your rating more).
The above scenario shouldn't happen too often, but a couple of game mechanics driven behaviors made/make it reasonably common. One was team selling. If three people who are capable of sustaining a 2000 rated 3v3 team wanted to make some cash, they could buy a fresh team each week (or worse, a low-rated 1300ish team), quickly win a bunch of matches in a row, get the team to 1900-2000 rating, and then sell it off for gold. The whole time those players are "farming" up the rating on that team, they are beating teams that are being penalized because they are playing a wolf in sheep's clothing. The worst part is that the biggest penalties are going to come to those teams that are matched against the team while its rating is lowest. Right before the team is sold, the "2000 players" are finishing up the last few matches at a 1950 rating. If they play and beat an opposing team with 1975 rating, it's not going to have mattered (more than a point or two) whether the team's rating was an accurate reflection of the players' skills. That same team from 1200-1500 is going to be matched against much lower teams and is going to easily win. Pity the poor 1500-rated opponents that are matched against these "2000 players" while their new farm team has a 1200-1500 rating.
A not-so-reliable indicator that this is happening to you is the opponents' gear level and arena-awarded titles. Full season 3 opponents may not necessarily be farming a team up to sell. They may just be running with some new friends, they could have just slowly accumulated points up, they could have bought points and be really awful players... etc.
Here's when I knew we were getting screwed by a team farming group. A few weeks back, we were matched against the same team 4 times one night and lost 19, 18, 17, 15 points in those matches. We were very frustrated, because two of them had Duellist titles and all were in good gear. They were obviously lower-rated than our 1550ish team, but were quickly gaining rating because the number of points we lost throughout the night kept going down. Two days later, we fought the same team again and lost 7 points. They had obviously taken a low-rated team and had very quickly raised its rating. The team name was..... "Teamz for Salez"... and since the people in it were actually Horde on my server, at the end of the week we saw the Trade channel filled with its members offering to sell a 1950-rated 5v5 team. Game mechanics changes will make this less of a problem, hopefully.
Point buying is actually a little bit of a help. Points buyers generally pay a team a big sum of gold to play 3 games on an already high-ranked team, most likely lose them, and have the really skilled people who are the "points sellers" play the remaining 7 games for the week. When the buyers play those three games, they will frequently lose (since they're not truly skilled as high as the team is ranked). This seems like a good thing, and it is if you get matched against a points selling team when the "scrubs" or "points buyers" are playing their three games for the week. The problem is, the buyers get onto teams with 1900-2000+ ratings, and you're probably not going to be matched up against them very often if you're on a team that's stuck down at 1500 rating. (It does happen, though-- if you armory a team that you win, say... 21 points off of, you may very well find it's full of awesome players who have played a lot of matches. It will also contain the guys you actually beat, who were the buyers just losing their 3 matches for the week). Preying off points buyers can be done successfully if you play at the same time they are playing AND you are rated high enough to be matched with them with any kind of frequency. If you're a new L70 team at 1400-1500 rating, this isn't going to happen much, however.
Anyhow... there's a little information about arena points, rating, and a little bit of (unsolicited) information about how some arena practices can impact the amount of rating you gain or lose each match.
Hope that helps!
