Be nice guys. You can deffend the agency without launching personal jabs at the OP.
I don't think this is a bait and switch, nor that it was bad practice from IF. First people do get sick, and since they work together it's feasible that they got their co-workers sick. We are in the middle of a pandemic, and it's a job that has inherit risk of other transmissible illnesses, that could circulate amongst them. We're supposed to stay home if sick, and you don't really want to see a girl if she's sick.
In terms of the girls going in to see other clients, in these scenarios it doesn't look like you had a confirmed booking with one SP. If you are just showing up to see the line up, that's not an appointment. You haven't committed seeing one of them, but have said that you will definitely not see at least one or more of them. It makes no sense for them to turn down a for sure client, for a maybe. When I've done the line up, there is always been a little variation from what I was told on the phone, but this was to be expected. Sometimes I've disappointing but not upset that someone who I wanted to meet has booked; but sometimes I've gotten a pleassant surprise that someone that I didn't know was available was.
With that said though, I have had some of the SP's complain about the new front staff, and I have witnessed some big errors. Once they listed a girl on their site at a time that is not her usual. I though I lucked out as it worked better for me. They booked a full day for her. When I arrived they explained that she was actually at her other job, and it had been an error. I later saw her and she was quite upset at the front staff, because she was worried her regulars that showed up for nothing were going to be upset with her. Conversely they once wrote the wrong date for one of my prebooking, and I got texts asking where I was at a time I didn't have a booking.