The picture of scientists politely discussing theories, proposing new ones in view of new data, etc. appears to be completely devoid of any emotions. In fact this is far from the truth, the discussions are very human, even though the bulk of the scientific community will eventually accept a single theory based on it explaining the data and making a series of verified predictions. But before this is achieved, does it happen that researchers fake results or experiments for prestige and/or money? How frequent is this kind of scientific fraud?
In its simplest form this question is unanswerable, since undetected fraud is by definition unmeasurable. Of course there are many known cases of fraud in science. Some use this to argue that all scientific findings (especially those they dislike) are worthless.
This ignores the replication of results which is routinely undertaken by scientists. Any important result will be replicated many times by many different people. So an assertion that (for instance) scientists are lying about carbon-14 dating requires that a great many scientists are engaging in a conspiracy. In fact the existence of known and documented fraud is a good illustration of the self-correcting nature of science. It does not matter (for the progress of science) if a proportion of scientists are fraudsters because any important work they do will not be taken seriously without independent verification.
Also, most scientists are idealists. They perceive beauty in scientific truth and see its discovery as their vocation. Without this most would have gone into something more lucrative. These arguments suggest that undetected fraud in science is both rare and unimportant.
The above arguments are weaker in medical research, where companies frequently suppress or distort data in order to support their own products. Tobacco companies regularly produce reports ``proving'' that smoking is harmless, and drug companies have both faked and suppressed data related to the safety or effectiveness or major products. This type of fraud does not, of course, reflect on the validity of the scientific method.