Would you accept a job which is not your line but pays high?

I am being offered a job that is too challenging for me as it's totally out of my line. I have no experience and my course was not at all anything related to it. It's more of marketing and very complex. The offer was real good especially considering that I am not even experienced to do the task. But the employer believes so much in me so he insisted that I accept it. Basic salary is way above regular plus there's going to be bonus for each successful proposal. Indeed, an offer hard to resist. Problem is, I will need to learn a lot. My fear is, I might hurt their business if I take the offer. Like going back to school. If you were me, would you accept the challenge?