The fact that the "written" some general rules, in fact, on any auction all depends on who sells and what sells.
Conditions can vary significantly (ie, that they overestimated their official interest in the case will most unloved their client will not take sin upon the soul - of this I have not heard
, but for pets to tame a new and promising customer or to get a picture in which he is interested, the auction house is substantial concessions).