found an article on good profit margins: http://www.investopedia.com/articles/personal-finance/093015/whats-good-profit-margin-new-business.asp
it depends on the industry. using that article as a guide, I would expect returns between 4% and 10%. The only people who get 20% interest are credit card companies and the ones who get 50% are your local loan shark and he quickly runs out of customers (or customers run out of fingers).
For an investment I would be happy with 3%. If you get rid of inflation (depending on your local currency/country) it would end up being between 1.5 and 2% which is decent.
Maybe I'm just being overly conservative or maybe I'm just happy to earn a little more than a typical savings account.