I don't know about high-level billiards, but low level billiards is basically synonymous with hustling and cheating (aka sharking.) Pool sharking is so widespread and infamous, I think it casts the entire sport in a sleazy light.
With baseball, a lot of high level players have gotten caught or admitted it, and have said that it's widespread. Jose Canseco admitted to cheating and claimed as much as 80% of players use steroids. He specifically accused Alex Rodriquez, which was later proven true. Allegations like these from admitted/caught cheats might be attempts to justify themselves, but personally I think cheating is and has been rampant in baseball for a very long time. It's still fun to watch though.
In case anyone is curious, Canseco played in the MLB from 1985 to 2001. It is unclear when the MLB banned steroids, but some possible years include 1990--1991, 1997, or somewhere around 2003--2005.
Note, however, that steroid use was made effectively illegal on a federal level in the United States in 1990. The 1991 date above references a memo from the commissioner that states that illegal drugs are "strictly prohibited". Steroids are mentioned explicitly, though they do not have to be, seeing as how they were in fact illegal.
With baseball, a lot of high level players have gotten caught or admitted it, and have said that it's widespread. Jose Canseco admitted to cheating and claimed as much as 80% of players use steroids. He specifically accused Alex Rodriquez, which was later proven true. Allegations like these from admitted/caught cheats might be attempts to justify themselves, but personally I think cheating is and has been rampant in baseball for a very long time. It's still fun to watch though.