After 10 years, the Green house block looks pretty much the same - nothing fancy, just a block you wouldn't mind living on. Renters come and go, the owner fixes what needs fixing and keeps the trim painted. Her tax appraisals show a gradual increase in property value. Appraisals on the Blue house stay flat. Several adjacent properties have followed the Blue house pattern and gone to seed.
Landlords find they can no longer get the same rent as before, so they're forced to lower the rent.
With less rent coming in, they don't want to spend as much on maintenance. The Blue house landlord cancels his lawn service and puts a clause in the rental agreement requiring the tenant to tend the yard. Then, because no one else is interested, he rents the house to a tenant who doesn't own a lawn mower. After 15 years, there's a noticeable difference between the Blue and Green houses. The Green owner puts hers on the market, and it's quickly bought by a young couple attracted by its well-kept appearance and hospitable block.