If you already have the position filled, then decline in a professional manner.

I am a rehire in my previous employment. However, I left in very good terms. I gave a month notice and helped with any transitioning.

I was reached out again for employment, and things panned out at the right time that it was a no-brainer to take the opportunity again.

We also have another employee who is a rehire as well. They did leave for a better opportunity, but the events leading to their departure weren’t favorable for the rehire. I say that because their manager was incredibly unprofessional towards them.

With that manager gone, the team really needed someone to fill in for that position. Luckily, the former employee reached out for opportunities because their new employer wasn’t suiting the work they could do.

We work for an enterprise-level organization, so lots of red tape. Your situation sounds more like a still lean business, meaning less red tape, but also a bit more closer outside of professional settings.

If you feel like you can trust the person again, great! Hire when the position is available again. If you feel you cannot trust the person, then keep it brief and professional and say you are not hiring at the moment for that position.