There's a lot of evidence. The fact is, he was definitely colluding with HRC the entire time. You can hear what his wife says on the Mic at one of his pre-concession speeches. It's clear they weren't serious about winning. Not only that, how could he sell out an entire generation of fresh-faced progressives and endorse the career criminal HRC?
If you want to see how a classy HONEST power to the people candidate does it, see Ron Paul in 2012.