The dog idea sounds great! How would i advertise it? I do have a dog but i could put him inside
to do a search for this yourself look up "pet sitters" or "pet sitting" "dog sitting" "dog sitters"
. They each have their own rules, some wont allow people who have already a cat or dog to take others in while others do. Some allow someone to take in many different animals at once from different owners while others don't. How these generally work though is the person brings the dog or animal around first for a meet and greet and then you decide or not if you'd like to look after that pet for them.
If doing this for a pet agency you wont have to even advertise as they just contact you when they think they have a suitable dog to stay at your place. Those places have a standard fee they pay the ones doing the sitting to take care of their clients pets.
For more of an idea of how you could go about doing this.. here is a couple when I search which will help show you how these work and how people just join up and do this
Pawshake . This is an Australian based site one but I thought there may be something like this where you are too which works same kind of way so check it out
https://www.pawshake.com.au/petsitters/adelaide-sa (this one it appears people are placing their own ads and isn't though a standard pet sitters agency as I see people are putting their own prices into pet sitters website. If you cant walk or throw balls much to a dog.. if your dog is cat friendly you could also look after a cat for a weekend or whatever and get paid)
MadPaws
https://www.madpaws.com.au/?gclid=CPvO5uqshcsCFZcRvQod4ooElA (this one is pet sitting through anothers business. they do the organisation, prices are set, they cover insurance if something goes wrong for the person sitting for them).
Anyway, you should have these around your area. As the amount of pay can vary for these sitting jobs through pet agencies, I suggest to check out the pay received of a few of them unless you decide to do it like as per my first link example.