(P)reviews.

I don't usually need either to decide what to buy but in the hypothetical scenario where both games appeal to me equally I'll go with the reviews. In fact, I rarely check the sales for games/systems that I don't have.

Reviews tend to be much more trustworthy in determining what games are good.

But, as opposed to music and movies, good sales do, generally, indicate a game is good. There don't seem to be many truly "bad" games that go on to sell millions. However, there is plenty of bad music and movies that become huge.

The 9.5 game easy. Exception would be if it was in a genre i don't like. Like car simulators or sports games. I don't blindly follow reviews though, but games like ME2 and UC2 which are loved by everybody is for the most part good. While Wii sports etc, sucks imo. I don't like these types of games even though they outsell all the GOTY material combined.

I dont trust sales as far as I can throw them. Just Dance does great #s but it is not very good to me. I trust reviews from certain places, (IGN, 1up, EGM, Amazon's customer reviews) for the most part game reviews to me are spot on, there are some instances where I dont agree (Goldeneye's IGN review score is too high, and the GI one is too low)

I don't trust scores or sales, I read reviews (both positive and negative) and try and figure out the gameplay elements and how well they are done and decide then, I decided I would hate FFXIII on a review that gave it a 9.5

Well we all know that you cannot trust sales, just look at the top selling games this gen-the call of duty games, absolutely in no way are they worth them sales so nobody should trust sales. Plus with sales products will sell more or less depending on price. What I trust is reviews but not necessarily professional reviews, I prefer to see what the average consumer score is because they'll be playing the game in the same way I am-at home as a my favourite hobby.

I don't trust any of them. Several of favourite games this gen failed in both reception and sales so...

I just read previews and watch gameplay videos to decide whether I will get a game or not.

Like others have said, read the reviews for some insight, trust the numbers to give you an idea if it has mass market appeal.  Try it out if you can or believe in the game developer.  Either way, it's a roll of the dice to me.  Very few games are actually worth the $$$.

If I would really have to pick, 9.5 game. From my experience, it has the better chance to be a game which I might like.

But in reality, I am not going to buy any more games just because they have great reviews. Games like SMG, Zelda:TP, Fable 2, GoW 3, MGS 4 and SSBB have thought me a lesson.