Valve bans developers manipulating reviews "all the time", and the practice is "really easy to spot", according to Tom Giardino, who works on the Steam Business team.
Giardino's comments came in response to Cliff Harris, the founder of Gratuitous Space Battles developer Positech Games, who warned on Thursday that online review systems were "fundamentally broken". Developers could illegally buy hundreds of copies of their own game "through shills" and then artificially boost its review score, he said on Twitter.
"I would never do this, but I'm not sure everyone is as honest. In all products/stores (not just Steam), review scores cannot be taken seriously without some heavy duty verification they are not shills."
In response, Giardino said that not only is review manipulation easy to spot, even if developers post the fake reviews over a long time period, but it's also not effective at boosting sales.