I'll believe it when I see it.In short, and this is not legal advice, just an observation from experience.

Don't ask me how I know but the best way to show the tenant what the problem is, is to remove the toilet, take it out into the yard, and proceed to bust it up with a sledge hammer while they observe (wearing safety glasses of course). 

When touring the property, use your scoping skills to observe how well the current owner has maintained the property and how well the tenants take care of their units.

Make it clear, section X of the lease states...I have observed XX on this date. 

To David's point, I observed the same phenomenon in Rochester at about the time I started liquidating my investments. 

My personal observations.

Yeah, I'm going to call out people who have poor power of observation and can't figure out that as most others have noted, this isn't normal wear and tear.

When it comes to these types of situations, be observant on how the contractor decides to handle things... it can be a big tell on whether or not they are genuine and are someone you should consider working with in the future!

I don’t make appointment to show the unit unless they pre-qualify.And I observe them touring the property.  

They want to see how good the lighting is because they forget to observe it, check the measurements, or maybe they didn't have enough time to really check the place out and get a feel for it the first time.