o you cancel the Appt or just dismiss it as some event not related to hobby?  

It got me uneasy seeing several police cars but fortunately it was a girl I've already seen before so I knew she's cool...  But what would you do if the girl isn't someone you have seen before

.... in front of a big Crystal City (Arlington VA) hotel i've been in on a few occasions who just generally roams around the hotels just because (no stings or any other serious reason .... very routine) and had a few freak the hell out. Only for the cop car to move on about their business 15 minutes later  .... awesome. -_-

Big hotels police have conferences, meet with security, could be handling an incident, or busting another girl that dudnt screen properly on rare occasion.  

Now a motel. Hell no!!! because I don't want police thinking im engaged in any other crime going on at that location or monitoring me. I aint lilly white and i'm not old so police take notice.

They park the cars there for overnight storage. IE they live in a different county than they work in. But buyer beware that could be indication of a hotel. I know one guy who got busted in such a hotel.

Most vice will be under the radar. You will never know or guess who they are. They won't be out and open with a marked squad car.  

Some places will do regular patrol rounds. It is not just for prostitution but to deter drug dealing and other bad things go do down at motels.

Even if a provider has seen you many times, I doubt she would have a problem understanding your hesitation. I would at least wait til police shift change after they left! Yesterday the lot of my hotel was overrun with police, which I later found out was in fact related to the hobby (apparently a robbery from what I've been told) - and just to avoid putting anyone in an position that may cause them to be so nervous, I decided not to take appts til wayyyy later after they left. I mean, things happen, police presence could be for a variety of reasons...but I can't think of a single one that I'd feel comfortable walking into!

If I saw several cop cars, I'd cancel or postpone, definitely.  I would see this as for her protection as well as mine.  She might not have known, having been busy in the room preparing for the appointment.  I know a few ladies who would ask why the hell I'd walk through cop cars to get there.  

If a provider would get mad at me for cancelling/postponing and warning her that her hotel is full of cops, it's someone I wouldn't have wanted to see anyway.

Even if they are there for another reason, they are trained to be observant.  She doesn't need them seeing me knocking on the door, and I don't need them seeing me coming and going right on the hour.  

That being said, I would be more concerned about a couple of unmarked cars slyly parked in the lot.  If they were trying to catch some fish, I don't think they'd make the hook that obvious.  

I am usually early to the appointment, since I have to allow for traffic that might not happen.  I use that time to drive around the lot looking for the orange EZ Pass boxes that identify government vehicles, or for people sitting in cars for no reason.

Finally, it doesn't matter if you had seen her before or not.  You have no idea what might have happened earlier that day.  John A gets busted trolling Backpage.  John A hands over phone and email.  Police use John A's credentials to book Provider B.  Provider B is stung, and police keep her appointments for the rest of the day.

I am not paranoid.  I am cautious.  I screen well, and expect to be screened.

not just to bust us. The odds are greater it is unrelated.

I'd talk with the provider and decide what to do together. Especially if I've seen her before.  

No panic, just work it out.