If the problem is vetting, really the best way is to get someone technical you trust (or with good reputation) to evaluate them. There are plenty of technical people whom you could hire for a day to give their opinion of any candidate.

However the real problem is usually finding the candidate and convincing them to want to join you. The people who you really want as a technical partner have a lot of other opportunities vying for their attention. You have to figure out how to stand out from the crowd.