Sometimes sites are cheating and just not caught like I remember a site did that, they used to skip the seeds somehow and scam site, while they were highly reputed. Can't recall their name but yeah truly trusted until then.
The site was DiceBitco.in although I'm not sure it's accurate to say they were highly reputable. They were a pretty new site that got lucky due a ton of traffic from the just-dice shut down.
I believe for this same reason we should more gamble on sports than in dice, because the verification system is quite complex and we can't just verify each bet using that long and tiring procedure.
This is why I like provably fair systems that can be machine validated. For instance the MoneyPot provably fair system is ideal for that (although, I don't know of anyone who had yet made browser plugins that verify that stuff), but I suspect seuntjie's dicebot would do that (just guessing though, based on the fact he's a smart guy who seems into that sort of stuff).
Or another good example is bustabit.com's provably fair, you can also validate it in real time (e.g.
a browser script you can run that alerts you if any of the games don't verify), as well as a bunch of 3rd party bots that are monitoring it