Powers and Authority of a Notary Public; Scope of Notarial Acts
The core powers
A Maine notary public may (1) administer oaths and affirmations, (2) take acknowledgments, (3) take affidavits and jurats, and (4) perform the other notarial acts the statute assigns - including certifying copies where the statute authorizes that act for that type of document, and solemnizing marriages. Notaries are also routinely asked to witness signatures and complete certificates on deeds, powers of attorney, and sworn statements.
Ministerial, not editorial
Your role is procedural: confirm appearance, identity, willingness, and that the certificate you complete accurately describes what happened. You are not a judge of the document's legal effect and not a legal advisor. If a signer asks "should I sign this?" or "what does this clause mean?", refer them to an attorney.
Scope limits
Authority is tied to your commission and to Maine. You may not delegate a notarial act to an assistant, notarize by telephone, or sign a certificate describing an act performed by someone else. You may decline to perform any act - refusal, without more, is not misconduct.
Traps
The biggest is confusing an acknowledgment with a jurat: the acknowledgment certifies voluntary execution; the jurat certifies the oath and the signer's presence at signing. Second, assuming the title "notary" carries any authority to give legal advice or to decide whether a document is legally valid. Third, assuming a notary must notarize for anyone who asks.