General Hypothetical on Implied Attorney-Client Relationships

Suppose someone consults an attorney (recommended by another party) to check certain regulatory or compliance issues and confirm whether a planned action would be allowed. The attorney does some checks with third parties and emails back that it looks fine and the proposed action should be okay.

Later, it turns out there were overlooked recorded restrictions that actually block the planned action (even though the main area reviewed was compliant).

Key details: No engagement letter was signed and there was no direct payment from the client to the attorney, any compensation may have come from a 3rd party.

There’s gotta be some liability here, right? If the attorney was asked to look into both the main regulatory side and overall permissibility of the action, but mainly stuck to the primary area before giving a broad “it’s fine” opinion, what are the general legal principles around this? Does the total lack of a formal retainer or direct payment automatically mean no attorney-client relationship exists (and thus no claim)? Or can a court still find an implied relationship based on the attorney doing the work and reliance on the advice?

Had a weird thought about this.