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Ask for code reviews where they explain the code line by line and overall approach.

Ask for detailed estimates and breakdown on a problem they never heard before, and insist on an initial approach to the solutoin, then verify with what is delivered.

When you do either of these, make sure there are experienced technical people asking questions. Anyone who is technical will not mind explaining code or solutions on the spot. At the very least there should be open conversations on approach, and usually you won't be able to hold that conversation if you are not doing the job.