Most experienced with dogs and cats, I've yet to ever live without a pet in my life. I grow attached to animals very quickly and their health and happiness is most important to me. I haven't got "official" experience with pet-sitting, but I've done it for many people
I've stayed a week at a co-worker of one of my family member's (who I'd never, and at this point still haven't, met or even seen a photo of) to take care of their two dogs; one a staffy and one a playful german shephard. Many of my friends have animals; six cats and four dogs between them all (as of currently). I've also I've owned two cats and three dogs across my lifetime. One of my guardians worked as a cleaner for a lady who owned two little pomeranian dogs that I looked after at the same time as my guardian cleaned the house
This is only an overview of the most relevant pet-sitting situations I've been in, in reality there are many more, so despite not having any "official" credentials, I do have a lot of experience!...