Tenant wants to sand/refinish deck

[Michael S.]

Unit is part of a 4plex. Each unit has a small (8'x10') deck on the back, maybe a foot or less off the ground. They are in fine structural shape, but are probably due for a refinish. 

One of our new tenants (have rented for 2 months) contacted us asking if they could sand and repaint their deck. Part of me wants to let them go ahead since it needs it, but I'm leery of whether the job will be done well. 

Do you guys generally let tenants do updates like this? If so, do you have them sign an agreement stating they will be held responsible if the job is left incomplete or worse off than when they started?