I don't really do Steam sales if I can help it (being a rabid anti-DRM freak). On the other hand, I'm part of the system, and I manage to obtain small amounts of Steam Wallet funds from the trading cards that materialise on my doorstep without my having to pay for them, so I may as well send those funds back to other game authors, right?
So this leads to the confusion of trying to figure out what to do with it.
I won't buy anything that costs more than $2. I don't have very much free money, after all.
I won't buy anything that I could get on GOG.com, because if I could get it there I'd far rather get it there. (I've already bought a handful of random gog games this summer sale...)
I won't buy anything that there is zero chance of me playing. Ugly 3D games are a no.
I prefer not to buy from a featured/flash sale because those are not the games that need my stray quarter. :)
I do read reviews - if it's broken or there's some other reason that it's a bad idea, I'm not going to do it.
This doesn't leave a whole lot. Right now I'm eyeing an adventure game that has 'meh' reviews and a little exploration platformer.