>No one ever takes time to write positive reviews of big businesses on third-party sites out of good heart

Maybe I am missing the context of big businesses, but I will often write a good review of a company (say on trustpilot) I have used, with no reward to myself. Even well known ones. The most recent example being Scan the hardware retailer in the UK. I have though also done it for reward too, so I am not completely altruistic!