While a lot of Sanders supporters see Hillary Clinton as a corporate shill who can't be trusted, in reality Sanders and Clinton don't actually differ that much.
The New York Times investigated how they voted during the two years they were in the Senate together. On 93% of the votes, they voted the same way. They did differ 31 times, though (7%) and the article lists every vote where they didn't agree. Clinton's voting record is comparable to that of Sen. Ron Wyden (D-OR) and Sen. Barbara Mikulski (D-MD), both liberal stalwarts.
Clinton and Sanders differed eight times on foreign policy and defense, mostly on Iran, Guantanamo, and the defense budget. Most times Clinton voted with overwhelming Democratic majorities and Sanders opposed them. On immigration, they differed seven times, once on Y-1 visas and six times on procedural questions. On the financial crisis of 2008, they disagreed three times. Clinton supported Obama on bailing out the banks to avoid destroying the financial system; Sanders voted with the Republicans to let the banks fail.
On energy, they differed four times. Clinton supported ethanol (probably because she was already thinking about the Iowa caucuses) and Sanders opposed it. They also differed on some loans and credits. On homeland security, they differed four times, all of which were close votes in the Senate. Three of them related to the conditions of issuing grants related to homeland security. The other one was about giving immunity to suspicious people who reported threats. Clinton was for immunity; Sanders was opposed.
The last five were a mixed bag. Clinton supported NIST's Advanced Technology Program; Sanders didn't. Clinton supported the FDA reform bill (2x), Sanders was opposed. Clinton opposed earmarks and Sanders supported them. Finally, Clinton supported $45 billion in estate tax exemptions and Sanders, this time in the majority, opposed them.