The lower g is, the lower the profit margin for s is, so so the fewer resources they will put into it. Unless there's unlikely to be more releases later or g are not cost sensitive and want it at a premium, this neatly scales to lower numbers.
Isn't it s/(s+g), where as you correctly say, g is legit account who want to buy? 1000 people want to buy a machine, 10 of them are scalpers, that's one percent on average? s = 10 and g = 990.
I am sure that Valve has some analytics they can lean on to try and measure how likely it is for an account to be a scalper/trading bot and it's also quite convenient for them that if they're describing their system as random they can sneak in some biases to help steer towards real accounts without making it easy for scalpers to glean what specific attributes they're weighting.
Yeah, I hope there's a gradient between scalper buying a single 99 cent game and actual person who has time played on multiple games and multiple purchases. The probability of someone with say a 3000 hours played across multiple games with hundreds or thousands of dollars of purchases is far less likely to be a scalper than someone with a single purchase many years ago and maybe some completely f2p play in say dota/cs, since the latter is likely to be a bot account.
They said the extra time ment they would be able to do additional verification. I’ll bet checking what games you purchased and play time are a part of that.