The best time to check a candidate's references is when you intend to present an offer, or when you're making the final selection between your top two or three candidates.
Reference checking should be used to determine whether a candidate has the credentials you think they have, and to ensure you haven't misinterpreted their ability to do the job. In other words, checking references is a mechanism designed to help prevent negligent hiring.
Candidates may also prefer that you seek references later in the process, so that their referees aren't contacted repeatedly when there's not yet an offer on the table.
Save yourself time and energy by only checking references of candidates you're seriously considering making an offer to.
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