I am a Rover sitter and a Rover user for my own dog and 2 cats. The sitter I usually use for my own pets raised her rates recently, but added a note in the first sentence of her profile that she had raised her rate, but would charge her old rate for prior clients. I think this is a nice way to do it. I would not mind her upping my rate, she is worth it, as long as I know ahead of time what I'm paying.
I myself have only been a Rover sitter since July, and I started with a lower suggested rate ($35). After my first two clients, I upped my rate $5, because the reality is it wasn't worth it for me to continue at the lower rate. I've had no problem getting new clients since then, as I'm still in the competitive range for my area. I've also rebooked with the first person, and she said nothing about the increase in prices, was happy to pay. If I upped more now, after having booked with 7 different clients, I would probably add a note to my profile. I think it's nice to offer a discount to repeat clients, but make sure you're making enough (minus Rover fees) for you!