I'm curious if there's any reliable way to check accurate sale figures for games in general.
I found [url=www.vgchartz.com]vgchartz/url], but it seems to miss entire entries or has pretty inaccurate sale figures for digital releases. Not sure how reliable it is at all.
Steamspy only works for steam, but seems otherwise some good estimate.

Anyone knows some better source? or just another useful one to supply (some of) the missing sales info?

Not sure why nobody ever answered this, but you could always go here:
http://www.vgchartz.com/
I hear that they're often highly inaccurate, but I also hear they get pretty close, so I can't tell you if they're reliable or not.

The problem is, no one really has accurate info since complete digital sales figures are not usually made public. A publisher might release numbers for a specific game, but not their entire library of digitally available titles and stores like Steam don't release numbers at all. The best you are ever going to get is an estimate, which vgchartz does provide.

If you're looking for (more) accurate stats, then only publishers can provide those stats. An example.