I have two cats and it doubles the price. For example, if the drop-in visit price for cats is $20 per visit, it charges me $40 per day ($20 for each cat). Other websites usually have the same price for up to 2 cats, and only increase the price %30-50 for additional cats.
if the visit is a drop in--and I only spend 30 min caring for both--I charge just for one animal---I tell client just to list one---
You should chat with your Rover Sitter. If I have a dog walk and there is also a cat, my rate is much lower as an add-on; however, 2 cats always shows as full price for both which I adjust based on my conversation with the potential client. Considering how many kitty visits I had over the holidays, I bet Rover will add a function so we can book multiple cats more easily without giving the idea that it is too expensive to have someone come in and look after 2 or 3 cats.
I have noticed that when a client with multiple pets requests a booking the automatically calculated charge is usually wrong, and I end up adjusting it down according to my multiple pet policy. Furthermore, it also depends on the provider's policy. Have a look at your chosen provider's policies and ask them about this matter.