If you're offered a research position but it’s not the perfect one for you don’t feel guilty for turning it down.

An interviewer will be polite if you decline a research position—and most will actually be grateful that you did so. Although that might sound odd, a research mentor only wants to work with a student who will be a good fit for the available project, and that starts with the student having a strong interest in the opportunity.

Therefore, if you discover during the interview that the experience isn’t the perfect one for you, the interviewer will be glad to know that he should keep his search open.
And remember, if you turn down the position in a professional manner, it's not being judgmental about the science a lab does--it just means it wasn't the perfect position for you.