I would check the date codes. Most of them will still most likelt be good but may need a new yeast packet. If you buy 1 get a new yeast but do a starter with the old 1 to see if its still good. This way if it doesnt start you are prepared to pitch a new yeast. You should always have a back up yeast handy.
As a rule the yeast in a wine kit is good for longer than the juice/concentrate. Recent yeasts have had 2011 expiry dates. Some of the kits I would definitely not be making in 2011 (but others might).
When I ran my store, I had sales for 3 reasons...
1) older kit. ask the retailer about the age of the kitr.
2) sale from the supplier.
3) sale at a slow time of year to attract business.
For example, in an FoP, sales slow down as Christmas gets close because customers cannot get the wine bottled before Christmas. I might have an advertised sale that incorporated kits on sale from the supplier.