According to few talks I had with people in the industry for popular trendy Youtube channel around 35% of views are fake, around 60% of advertisements views are fake.

For channels related to companies or during product release date or important event number of fake views reach 80-85% and numbers are closely monitored by company that had been hired for promotion.

For growing channels related to ad agencies, retailers or large companies (usually it made look like it is individual bloggers content but with lot of very expensive items and with superb sound and video level) - fake views are around 60-70%, fake subscribers at initial stages does not fall below 60%.

Of course, none of big guys is using simple cheap techniques for this. Most views for large channels will be provided by hacked routers and smartphones botnets, for growing channels it can be real human operators (one operator do 10-25 views at once) working via similar hacked botnets as relays.

Most expensive are real people who imitate normal behavior (no more than 4 parallel videos) and they are mostly used for initial subscribers base as they need to react to new videos on channel and post commends according to provided requests.