Agreed also about the clacks as an investment thing. But honestly I haven't seen a lot of immediate turn-around classifieds threads lately, there seems to be a lot more trading going on now a days, which is just fine by me. It's a good thing that those who clack-flipped immediately after sales are chastised the way they are, but you can't lump them in with every other type of sale.
As for big sell-offs, isn't that the end pay out? Sometimes you grow tired of something, or outgrow it. If you know the rough AM value and are looking to sell off a collection you shouldn't be stigmatized for it, and you should get what your collection is worth not what you paid for it. I think that's a totally legitimate thing to do.