A general power of attorney that only covers day-to-day banking will usually not be broad enough to sign a listing agreement, accept an offer or complete a closing on someone else's behalf, so check the specific wording rather than assuming any power of attorney will do.
This comes up most for a family selling on behalf of an aging or absent parent, and setting the right document up before a health event forces the issue is far easier than getting one signed after capacity has already declined, since a power of attorney signed after that point is not valid.
Budget legal fees of $800 to $1,500 for the review on top of the usual closing costs, since this is not a step a lawyer will skip. Get your hand-reviewed valuation from Joel Dyck.