If one untidy neighbour is all it takes to drag down the value of all the properties around him, it just shows that the entire market is over inflated and built on smoke and bullshit.
What makes you think you're entitled to these higher values?
Well, the housing market is bad, sometimes very bad, in many locations.
It's not just a matter of value, but of how long it now takes to sell a house.
So, yes, one untidy neighbor could be a problem when trying to sell.
My next door neighbors were trying to sell their house a couple of years ago. My other next door neighbor who is mostly out-of-town (independent long haul trucker) had started construction on the front of his house but it drug out a long time. The neighbors trying to sell offered to pay for a contractor to come in and finish up his project.
If people are willing to pay money, they sincerely believe it to be a problem whether you or others think so or not.
Fern