I bought an airplane from a chap who was in a nursing home. His wife signed
it over to me with a legal power of attorney. The power of attorney was
completely legitimate and I had supporting documents.

The FAA did NOT accept the bill of sale. I finally managed to get a
scribbled signature of a bill of sale and get it registered.

( he was in the final stages of Alzheimers)

Cheers:

Paul