General question from non-tech person

I have a question regarding random number generators. Is it possible to truly have a random number generator? I have heard no matter what that if you dig deep enough that you can predict (within certian percentages or ranges) what will come up.

Example was an ex-slot machine manufacturer employee was able to crack the code on the keno machine to predict what numbers were coming based on the numbers from the last game. He said it only gave him a 3% chance of being correct, but he did it 10 times and it gave him a 30% chance to be correct. He said he hit it on the 1st try.

My question is are there any true random number generators? Or are they all flawed in this way?

I am not a programmer at all and will not understand any programming language or code.

The reason I am asking this is I play online poker and I am trying to determine if I am playing a fair game or if it is possible for a good tech person to exploit these weaknesses.

Thank you in advance for any responses.

Generally it's correct, but without knowledge about algorithm you can't make a prediction, and there are many much less 'pseudo' random data that can be used as starting point in random generators. No chance if all done even a bit properly. Most of vulnerabilities in such games are concerning "management prizes". Say, only for first game or first win you can get 2 times more. Such conditional modifiers can be missed by game manufacturers, and if you will play some uncommon way you can gain average positive balance, say you play only one game for account (create new account for every try) and can get double prize for first game, then you will win on average.