Some might be made up, but not all. There are many eyewitness accounts from reliable people like forest rangers. So, it's hard to say all are false.
Not entirely. There have been cases where people have reported seeing a large, hairy, bipedal creature in areas where it's hard to explain what else it could be. However, some stories are likely exaggerated or misinterpretations. For instance, a large bear in the dark could be mistaken for Bigfoot. But the fact that so many people claim to have had encounters with something that resembles Bigfoot makes it seem that there could be some truth to at least some of the stories.