I agree that scientists are human and thus are prone to greed and other less an reputable actions. But
its almost impossible to produce lasting but fraudulent work in science because other people have to verify your work. They have to independently produce your results in their own labs or witness the same phenomenon. There is also peer review where anonymous scientists in the field are PAID to find every little problem they can find and report back on it.
Is it absolutely perfect? No. For example, pilt down man, cold fusion, and the cloning fiasco with Hwang Woo-suk.
The problem with fraudulent scientific work is that it all deals with the real world. If people can't verify your work in the real world then your work is discredited until someone can. This is exactly how all the above hoaxes and frauds were caught. No scientific claim is taken on faith.
Its possible that evolution or the theory of gravitation could be wrong. But its unlikely given the enormous amount of evidence in support of them. Minor revisions and changes are possible and expected (such as the effects of relativity) but massive paradigm shifts are unlikely. After all, if we had already figured everything out in these fields then we wouldn't need biologists and physicists, we'd only need engineers.
On a side note, I'm not a biologist. I'm an computer engineer. So I don't know all the nitty-gritty details of evolution nor can I defend evolution for very specific and narrow criticisms. I don't spend much time discussing evolution beyond the basics nor do I care to. There are a few biologists on this board who can address those or I'm sure there are plenty of books that can as well such as the book I mentioned earlier. Talkorigins.org is also very well known and reputable resource.