Not necessarily depending upon your state. Recording does put the public on notice, but your POA should still be effective. Be sure to bring your POA to the Trustee's sale. If you would like to be overly-cautious, you would likely record the POA with the county Auditor in whatever county the sale is occuring and/or the county where the property you will be bidding on is situated.
Excuse my edit but after review, the POA should be recorded and should be done so in the county where you reside. Also, be sure to record a revocation once the special POA has run its course.
My colleague is correct about recording the POA. Your agent should bring a recorded copy of the POA to the auction. You should call the trustee and confirm that they will honor your agent's authority with the recorded POA.
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