... And, has their movers literally pile boxes to eye level over every square inch of the 600sqft unit, save for a 12" path from bedroom to bathroom to kitchen.  Fish tanks, boxes of stuff, things they bought and intend to resale, and lots of ... stuff ... that has no practical use in a 1 bedroom apartment.

You did your standard screening and everything checked out.  Retired couple, fixed income, references check out, involved in the community, nothing negative on credit report.  You discussed decor with them and their vision for how they'd decorate and helped them measure the rooms so they could pre-plan their furniture.

And, still, boxes and boxes and boxes of stuff.  I had one unit where such a situation caused all sorts of problems - cockroaches because they couldn't clean adequately, mold on walls because couldn't circulate, leaking I-don't-know-what from a box  that damaged the floors.  Not going through that again.

How would you approach this? How long would you let them "settle in" before laying down the hammer?  There's a "safe living space / no vermin / tidy / no clutter in the yard" clause, but nothing that specifically says "Thou shalt not hoard."

Unlikely someone with this behavior will change, but how do you give them a fair chance while protecting your options as a landlord to protect the unit?