While I agree with the rest of the statements, I consider using this technique more often.
When one sells a domain on NP, he is looking for a quick "reseller" pricing. If in any case the domain does not sell, he is putting it back in the vault.
When a serious end user comes, it is likely he will do a research on the name, and if he finds out that it was for sale on a forum for $50, he won't offer you much more, even if initially maybe he thought he would pay $xxxx.
So, personally I will take care that my domain names that I offer for quick sale on forums at bargain prices will not be indexed by search engines.
Is this really your picture?