I looked into this for Canada, and my understanding is that it wouldn't likely hold up in court if you were doing all of these activities concurrently, but I'm not sure that was what MMM was doing. I understand that to be deemed as separate from your person, the corporation would require a separate bank account and it's own set of books. Incurring business expenses also seems to be highly relevant, so in that case the computer repair business could run into trouble if you are deemed to be delivering a professional service, but the coffin business could be more defensible as it would require materials, other labour, delivery services etc.... Additionally, I understand that for the corporation to be defensible, it needs to be adequately capitalized for the business to be done with it, and all profits and losses shouldn't be directly transferred to a sole owner.