A witness who has known everyone involved in a transaction long enough to verify he knows that each person is who she says she is and is an uninterested and objective party can witness a legal document, notes the Law Dictionary. The witness must be of sound mind.
A witness should have no financial interest in the situation and should also be trusted by both parties, says the Law Dictionary. It's common to select a notary public, certified by the government, as a witness. The notary places his signature and seals the document with a special stamp. A bank officer can also act as a witness, especially if there's a risk of the bank being held liable when fraud is discovered.