What do the reviewers do? They don't try to reproduce it. So yeah make shit up, as long as it is plausible no one will notice.
For example Yoshihiro Sato was recently (2016-2017 time frame) caught fabricating results, turns out he had been doing it for 30 years. He had more than 20 papers retracted. Also note he wasn't caught by a fellow scientist in the field he was caught by a statistician bulk processing papers looking for anomalies. So yeah big penalties if you are caught, but the odds of getting caught are so low you have to be stunningly stupid to get caught.
Sadly, once the statistical methods being used here and the types of anomalies being found become well-known, it's probably not too hard for fakers to adjust their "results" so that such anomalies are far more difficult (if not impossible) to detect. For example, if an analysis would show that your experimental data is maybe a bit too clean, in a way that wouldn't normally turn up in the real world and would therefore cast doubt on its validity, then you just need to make sure that you dirty it up a little before publication.
For example Yoshihiro Sato was recently (2016-2017 time frame) caught fabricating results, turns out he had been doing it for 30 years. He had more than 20 papers retracted. Also note he wasn't caught by a fellow scientist in the field he was caught by a statistician bulk processing papers looking for anomalies. So yeah big penalties if you are caught, but the odds of getting caught are so low you have to be stunningly stupid to get caught.