[SlowMowTurf]

Who are you potentially working for?

Someone may "give" you an old mower that may/may not work? (screams "Hope I can sucker him into working cheap!")

I've never run across a renter that wants to sink money into improving someone else's property.

I've never run across a landlord that wants to sink a penny into improving their rental property because every penny spent beyond the absolute minimum is lost profit.

Looking at the photos suggests the same - no money or effort has been put into upkeep.
I would be surprised if anyone involved will want to pay what the job is worth.

All valid concerns.

Bad Boy zero turn for free? Bad Boy is frowned upon in these forums for the most part, but come on - free?
Sounds like the client may be the renter, NOT the homeowner?

I do bi-weekly mows for a renter and the renter pays in a timely fashion. It's completely clear to me who I'm working for- the renter, not the owner. Somehow it's part of his rental agreement. Make sure who is hiring you/responsible for payment.