Let's say I want to be in the google top 10 on the phrase 'casino'. Logically i write many articles with anchor-text casino, however i heard that it can affect the site in a bad way is that true?
If you are loading your articles with useless keywords, it could affect your website status on Google. It is called keyword stuffing and it is frowned on by Google. However, if the words flow with the article, there should be no problems. Now anchor text is a whole different thing. Anchor text mean you are placing links somewhere. If you add the keyword link in many articles you submit elsewhere, that is what you are suppose to do. Just do not overload an article with several of the same anchors in the same article.
I always like to vary the link text using the main keyword I'm targeting. So in your example I'd use link text like, "online casino", "land based casino", "fun casinos", "best casino", and of course "casino". Make up a bunch of variations that relate to the content of your page and switch off using them. This looks a little more natural to the search engines.