@mapozi - It might be very rewarding or very frustrating to work for an individual. It all depends on one thing - the personality of that individual. You have to research thoroughly the kind of person this multimillionaire is. This is easier said than done because most current employees will not be honest with you because they don't know you well and most ex-employees - especially if they were fired - will give you real and imaginary negatives (only) of the person.
I don't know how you will get this information but without it I would be hesitant. There are fellows who are totally confused themselves - despite or because of their millions, change moods like..., have no respect, might wake up one day and fire you on the corridors or tell you to pick up/drop their mistress etc. etc. On the other hand, there are fellows who are very understanding, patient, nurturing, respectful, will teach you the ropes and will totally change you for the better. And then there is everyone else in between. You must identify what kind person you are going to work for BEFORE you quit your current job. In a case where you don't have a job, you simply jump in and understand the person with time - you have nothing to lose after all - you can always quit. But you have a job.
Lastly, as @mukiha asked, what's your passion? Where do you see yourself in 10 years? Which of the two jobs is in a line with these?
Never count on making a good sale. Have the purchase price be so attractive that even a mediocre sale gives good returns.