I’ve been doing this on the side in Astoria for about four years, mostly word of mouth in a couple of co-ops and a parent group. The short answer is yes, people absolutely hand over keys, but you need a system. I never put a client’s key on my own keyring with my name or address attached. I use a small key wallet or a labeled envelope that stays inside my apartment. If they’re comfortable, a lockbox on the apartment door or mailroom is even better.
Meet and greets are non-negotiable for me, even for a neighbor. You want to see where the food actually is, what kind of cat you’re dealing with, and whether the place is clean enough to sleep in. It also protects you from the 'the plant was already dead' claims later. Take a quick video or a few photos of any existing damage, and confirm in text what days you’ll be there and which keys you have.
For one cat, I’d avoid quoting an exact number without knowing the neighborhood and whether you’re expected to stay overnight or just drop in. Some people charge more for medication, multiple visits, or carrying mail and rotating lights. If you’re just starting, undercutting the big apps is fine but don’t do it for free. Friends can turn into clients if you set the rate before the trip, not after.