You interview them, just like we do for every unknown person. If you don't want to take the time to do that, then you do a quick search for work they've done,

You interview them, just like we do for every unknown person. If you don't want to take the time to do that, then you do a quick search for work they've done, and then come back to the 'do I want to interview this person?' question. Ask them what their timeline for having a job is. Tell them that the interview will involve coding on this specific thing, give them weeks or a month to prepare for it. Help your candidates do the best they can. Don't set them up to fail at a task they weren't expecting.