They are fair and you're probably just mad. Stop thinking that you can make money out of such websites. They are there for entertainment purposes and not for you to get rich.
Others have also said similar things in the past and they haven't been really right (yes, we've also had websites that were cheating). You can't generalize this. There are ones that are provably fair and that do not manipulate your bets.
Even if you play on a 50% win chance, you might have a lot of losses in a row.
Here's in a thread related to PD:
https://bitcointalksearch.org/topic/is-primedice-really-provablyfair-253144
Topic: About DIce Provably fair. (Read 308 times)
Are you verifying your rolls? You can check if they're cheating. What site are you playing on? Could be a scammy one. I'd use a popular one like primedice or something.
Well all BTC dice sites and casinos say that its provably fair system and only house edge is their income.. if its so why the hell is that when u bet 1 satoshi u have higher win chance then when u bet 10,000 
for example you bet 1 satoshi on 1.1x payout (90% win chance) and play 100 bets you win 70-80 times for sure and if u play same payout with 10,000 satoshi u win 30-40 times no matter how many times u test it result is always same provably fair yeah for sure.. thats bs.. 
for example you bet 1 satoshi on 1.1x payout (90% win chance) and play 100 bets you win 70-80 times for sure and if u play same payout with 10,000 satoshi u win 30-40 times no matter how many times u test it result is always same provably fair yeah for sure.. thats bs.. Jump to: