@Sheri76 Trouble is, your listing does not appear to have any rules concerning unregistered guests/visitors. This is a thing you need to fix immediately if you don't want guests to take the liberty of bringing any number of visitors onto your property for any reason. My text would be: "only the guests named and registered in the original booking are permitted onto the property. No additional visitors are allowed at any time." Even if that seems harsh - having a clear rule without loopholes gives you the power to make exceptions on a case-by-case basis with guests you trust, and a more airtight case for termination if a guest breaks the rule.
I don't think it is or should be relevant whether the guest's visitors are app hookups, friends, or colleagues, because it wouldn't be reasonable to micromanage which types of (legal, consensual) socializing the guest is doing. The message you received addressed to "Rick" might be a red herring (why would a social media contact write to the guest's Airbnb host?) so I'd ignore that.
Since you didn't have a rule in place at the time of booking, you'll have to bring it up directly to the guest. Communication is key here - tell him that his previous review raised some concerns. and you just want to make sure he's aware that as a one-person booking, he is the only person that you're permitting to access the home during his stay. If there's any sign that this is a problem for him, I think it would be fair to offer him a chance to cancel for a full refund. It would have been better to get in front of this well before his arrival, but it's not too late.
As to the question of whether you're paranoid? Well, look through these forums and you'll see stories from hosts whose homes have been used as brothels, meth labs, extreme party houses, drug dealerships, fetish dungeons, and any number of things unintended by the host. Even though most guests won't be problems, it's still important to have clear, firm rules and be prepared to enforce them.
