Ah yes,, the behaviors you've described falls under the much discussed topics of Separation Anxiety and Marking. You may want to search each of those terms to see all the contributions.
Even a dog who is house / potty trained may lose it's ability to act the same way the dog would at home. Same goes for anxiety behaviors of being crated away from home. This is fairly common because the dog has left the comfort of its' home, its' family, and is in a stranger's home with strangers and possibly other pets. Unless the pet parent has had another pet sitter in the past, who told them how the stay went (many times sitters will not be 100% forthcoming of the issues out of legitimate concern that the pet parent may get defensive and leave an unfair negative review score/comments), the pet parents very likely have no idea how their pet does away. On a side note, I wish Rover suggested the following to everyone before first booking.
To solve the peeing and marking indoors, there are a few options.Some retail pet stores sell belly bands (for males) and diapers (unisex). Of course, they're also online if you want to stock up in the future. You can also make a belly band or pet diaper on your own. For a diaper, you could go to a drug store, buy baby diapers for weight of the dog, figure out where the tail would go through and mark the diaper, take diaper off and cut a hole where you marked, place diaper on and thread tail through the hole. Alternatively, you could get some child size or stitch some panties smaller to fit the dog, place a panti-liner inside (change as needed), and put the underwear on the dog while in the house. A belly band id basically a strip of fabric which has absorbent pad or gets lined with a panti-liner, with velcro closure. To create belly band, you may be able to use knee high sock, panti-liner, and then find a way to keep closed that won't injure dog.
The other way to handle it is to get either a baby gate or pet gate or pet playpen fencing (tall enough that the dogs you'll book wont be able to jump over) and place it on a more easily cleaned floor such as tile).
BTW, for future stays you may want to consider discussing a shorter stay (as in 1 overnight or even 1 daycare) with the pet parents at the meet&greet for the benefit of all (the pet, them, and you) to allow you to get to know each other better.