"Marking the close"

For those who've never heard the phrase, it's a form of market manipulation where if one has, say a large position in stock, for margin and profit and loss calculations one may buy a small bit right at the close in a sloppy manner, possibly overpaying a bit, the position will be "marked" or valued to that sale. It's illegal and policed for in many financial markets, but it seems like there are... [more]

For those who've never heard the phrase, it's a form of market manipulation where if one has, say a large position in stock, for margin and profit and loss calculations one may buy a small bit right at the close in a sloppy manner, possibly overpaying a bit, the position will be "marked" or valued to that sale. It's illegal and policed for in many financial markets, but it seems like there are shades of it in real estate. When a developer sells a unit at some price and does a huge concession on the backend, I presume his building and other comps are marked to the sale price, not taking the concession into account. I'm sure some of this goes on, but in people's professional estimation how prevalent is it? It seems like it has the potential to skew comps considerably. It worries me especially here in the financial district. Am I overthinking it? [less]