I could be blind, but I did a rough scan for this on the suggestion pages and I haven't seen such an input on the members section either, so I thought it was worth a shot to suggest this.
Sure it's only a minor thing for you American's but when you live half way across the world, the 12hr offset between when you say it was sold on Nov 8th, when it was actually Nov 9th for me is just a tad bit annoying.
Stop being behind the times :P
Anyhow, I'm hoping that you guys are storing the dates as UNIX_TIMESTAMP() or something closer. If it's being piped straight into the DB as date('M jS') it will be impossible to do. Giving an offset where the value is stored and then added to the times before you throw it into date() or what ever custom function you use, would allow players to give the sales history a more accurate time listing based on when it actually happened locally.
Yeah I'm annoying and suggest all the little fiddly things rather than large grand scale features :D