Originally we tried creating an account for people who create original content, posting some of their work under that account, contacting them to show them how much they made and then we would turn the account over to them. That didn't work out so well to date since no one has responded to our emails.
We believe it's because people see an email saying you can make money doing something and they immediately assume it's spam and don't fully read or grasp how easy it would be to claim those funds.
So now we will simply donate all proceeds their content earned directly to them in Bitcoin (usually) and email them as a donor and let them know where all of that juicy BTC came from (Steemit) and that it came from their own work in an attempt to bring them here. We feel that they are more likely to read an email from a large BTC donor (large for a single article donation) letting them know how the funds were earned. :)
pardon if the answer is clear somewhere else, though I'm very new to the platform...
are there specific guidelines published anywhere on the protocol for posting others' content?
i.e. if we're sharing content we didn't create, what exact details must we include to specify it is syndicated and not original content?
if there are such guidelines, where are they to be found?
You're asking the wrong person about guidelines. I generally don't follow them if they exist and they are usually created after I've done something others find offensive. Regardless, this is a blockchain and there are no rules. Make your own rules and see what works for you. This is a popularity contest. We could post the same thing and you could make thousands, while I would be downvoted into oblivion. If you want to make $$$, pander to the whales! Just don't point out the obvious pandering publicly or you will not receive the whale love. Let me be your living example of how not to behave on Steem ... if you value money over integrity. :)