I typically research a Witness before voting for them. Now. When I started off here I didn't do that, I voted for whomever. Most witnesses for whom I have voted I have interacted with and know some of their goals. If those goals change drastically and are no longer in alignment with what I support for Steemit, then I can change my vote. It,s good to actually talk to witnesses and comment on their posts. The human interaction makes a big difference in the building of trust.