Like Karen said, even if your rates are set high enough that you would be taking home $500 a week when fully booked, the likelihood of being fully booked is slim to none, especially when you are first starting out. Beyond that, you have to consider that this is taxable income, and come April you'll be required to pay taxes on your earnings, at a rate of 15%.
Take home income: 500/wk x 52 wks = 26000/yr = 15% tax bracket regardless of how you file
True earnings (including fees paid to Rover): (500/.85) x 52 = 30588/yr = still 15% tax bracket
And again, that's assuming you stay booked with two dogs at an absurdly high nightly rate for all 365 days a year. You would never get to go away for a night during that time, let alone an actual vacation. You couldn't even attend all day events in your own town because you'd be responsible for someone else's animals.
To compare, this is something my partner and I do while I work full time (3 12 hr days/wk) and he's in school. We host maybe 1-2 dogs per month. December has been by far our most-booked month, with two dogs staying with us from mid-December to early January. Each is paying us $25 per day with our extended stay discount (normal rate is $30), for 16 and 17 days, respectively. After Rover fees, we'll actually get about $630 for over two weeks of full occupancy. It's a good supplemental income, but until you're established and have a solid client base and a reputation that allows you to charge above average in your area, it probably isn't going to be a good reliable full time income source.