I haven't heard of an official ruling. And short of litigation or defamation you really can't stop that Realtor from linking to you.
If there is a reciprocal link, I believe you very much into "a thing of value" or you'd have to justify a marketing exception. But if they simply link to you, I don't see the likelihood of a Sect 8 citation. This assumes you don't have some special relationship with the Realtor for referring business to you. It sounds like they're looking for a local flavor and perhaps to gain credibility off your reputation.
You're free to ask that you not be linked to. You could have counsel send the letter for emphasis if you really don't want it. And you could have some content at the landing page that "we are not affiliated with the XYZ Realtor and have requested they remove the link to our site..." The next question is, do you want to do any of that?
Just as lenders get thrown into directories of different sorts, I might categorize this, as one of those. So accept it, but don't encourage it, ask that it be removed, post your own disclosure, or consider legal action. Personally, I would accept it, but not encourage it.
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AndyZ CRCM
My opinions are not necessarily my employers.
R+R-R=R+R
Rules and Regs minus Relationships equals Resentment and Rebellion. John Maxwell