It is illegal to pay someone who does not have a business license to pet sit, house clean etc. Call it whatever you want but if the person trips and falls at your house you are liable. When you hire someone, you are responsible for their wages at minimum wages + overtime, payroll taxes and workers compensation. Pet sitters are never independent contractors, unless they own a business license which makes them an employer. Someone is always an employer.
We don't pay under the table for that reason and we always use an agency which employs their staff, for pet sitting and cleaning. Even for handyman, we make sure that they show us their business license.
We were paying pet sitting at $40 for a 20-minute visit for about 2.5 years with one agency and late this year we switched to one which charged $20 for a 30-minute visit, for 3 visits a day. We supplement this with friends who drop by and after we come back from trips we take them to fancy restaurants for dinner so that no money is paid directly to them.