All campaigns run their own internal polls, and they use voter files, not random samples. They know what every voter on file is likely to do in every swing state. Every single voter. They likely use public polls to confirm their numbers, but their numbers are likely much more accurate. So if you want to know if public polling is accurate, check out the actions of the campaign. Hillary is sending people into Utah, Arizona and Georgia. She doesn't need any of these states to win. Trump is sending Pence to Utah. That information should tell you something. Recent polling has shown Utah, Arizona and Georgia as very close. The actions of the campaigns seems to confirm that. Trump campaigned a couple of times in Texas, which seemed odd at the time. Recent polling has shown he's only up 3. Their internal polls probably confirmed that.
Also, a good way to check enthusiasm is not crowd size, but higher incidents of new voter registration. 538 recently reported that they have not seen a big swell of new voters on the republican side that would indicate Trump turning out the "hidden white vote". Maybe he will, but the evidence isn't there.
There is also this new report from WaPo of Trump ending major fundraising for the party. These are not the actions of someone who is going to win, or even thinks he's going to win.
Link: https://www.washingtonpost.com/news/post-politics/wp/2016/10/25/trump-halts-big-money-fundraising-cutting-off-cash-to-the-party/