It really is very important to meet with your client beforehand or at least know the area where you will be sitting in. I am still very new but my first client lived in a really nice gated neighborhood and both of his dogs took a liking to me and I felt secure. My next booking is for a nice couple my age, also in a nice, gated-like community. My other request is from another couple that lives less than 5 minutes away from my apartmentment. I would never feel comfortable asking an owner to let me have a guest, as they would not have a registered background check like me and I wouldn't want to make the owner feel uncomfortable in knowing I wasn't confident in wathing their dog alone. Always get a read on someone and their pet before you commit, and it doesn't hurt to have someone you know close by knowing your location and checking in with you periodically. If it really makes you that uncomfortable, just stick to check in visits where you can have a friend waiting for you outside the owner's house. Goodluck!