Do casinos operate in a fair manner in reality or they just pretend to be honest? I know that there are reputed online casinos operating from over the years but I want to ask that what is the credibility of an online casinos that they don't cheat while generating results.

Online casino or poker rooms operate with the support from software. So it becomes very important for online casinos to make sure that their software is trustworthy and ensures fair play. There are certified agencies and organizations which inspect, audit and certifies these software. Furthermore they ensure that software is fairly coded with a stable structure and RNG (Random Number Generator).
Also you should try to read reviews about casino software as they are tried and tested there.

Just like in any industry, there are “goods” and “bads” in online gambling industry too. Having gambled at online casinos over the years, I would say that one should try to play with top or reputed online casinos. They operate in fair manner and have reliable and trustworthy software certified by independent third party. Reading reviews about online casinos would help you in separating fair and foul casinos.

And there are lots of bad casinos out there that are not honest at all. That is why I think it is a good idea to stick with well known "good" casinos with the major software providers to avoid any kind of fraud.

It is very obvious what you said. But if you take a look at number of fraudulent cases and allegations, it is getting hard to search for “good” casinos.

It is not “hard” to search good online casinos provided you search at correct platforms.There are lots of good and reliable online casinos. The site also has a good collection of articles and reviews.