It is well known that all online poker rooms are not honest, they
are created to steal players' money. It is enogh to look for example to
the discussion here:
Are most online poker sites honest? | Answerbag.com

And among worst poker rooms in this respect is the William Hill poker.
They use extensively the system of false "players", figures which
you can see at tables which do not correspond to real players, but are
just software tricks. It happens too ofthen at their tables that one of
real players gets some really good hand, put big bets but looses against
an even better hand of this false softwere thrick.

I storngly recommned to anyone not to give your money to William Hill,
it is a very corrupted room.

"Basically the system uses sock-puppet accounts, monitoring the behavior of other players on a massive scale. It builds a database of their habits, and chooses patterns which are predictable to select it's marks. The marks are then targeted by human users, and the humans are given guidance by the computer so that they can play with full knowledge of that person's habits." -- StableBoy

That sounds crazy/silly but I can see it happen. The part that makes the most sense to me is the "behavior/habit patterns" database. I heard that's what online casinos use to cheat the players.

I dont know about william hills site but thats a big book maker in this part of the world and i highly doubth that they would use such software. And there are independent reviewers of the RNG software they use if there wasent they would lose there licence. And if they are doing it then every site would be at it i reckon.

I do think that all sites lie about the number of players on for a good honest gauge of traffice check out Online Poker Traffic Rankings & News | Poker Sites & Networks | PokerScout