Generally on Wednesdays....
No, seriously, my "danger sign" is when I have been through a dry spell or I go to a show and find little that I am interested in. It's sort of a "girls all get prettier at closin' time" mentality.
Realistically, I am most likely to "overpay" for the things I get cheaply...you know sometimes you say,"I really don't need that, but man, that's just too cheap not to buy." So you pick it up and then it lives forever in a shoebox without being looked at or appreciated again.