Just spoken with a potential client and on two separate calls he asks me if I'm by myself at the suggested meet... is this a red flag for anyone else?
As a precaution I did decline the booking btw 

Yes, those kinds of privacy/security questions are red flags. I immediately bin them, and just for laffs I often ask why they want to know? ...to see what they come up with.

Be carefull from this kind of ppl, it happened to me once. The client asked me if i was by myself and  i said yes, but I have not notified that it could be dangerous.  I booked him for 1 hour, he came and started to have his eyes everywhere, like he was looking for something, he was taking his time he did not know if he wanted 1 hour or 30 minutes it lasted  5 minutes, I think the worst of my life.  then I asked him to leave and I pretended to call someone to scare him.  never accept this kind of customers because : 1 they waste your time and 2 they have a  bad intention

If a potential clients asks that even once it's an instant block x

I concur with others I wouldn't see anyone who asked this. My feeling is that guys who are worried about bumping into other clients or escorts ask the more generalizing and less creepy question "is your place discreet?" Because at the end of the day, it doesn't matter to them if there is someone else on the property, such as a friend watching out for us or another escort, as long as they don't have to run in to them or have it effect their booking.

It may just be a client who is too stupid to word it in a less creepy way who hasn't locked on to the fact that we are vulnerable in our jobs and have to be cautious, but how many attempted bookings will he get turned away from because he is "coming off wrong" before he gets the picture? Red flag for sure, either total idiot at best or possible thief/abuser at worst.