Periodically, Bigpoint (the designers of Battlestar Galactrica Online) will announce various in-game sales. These will be to specific types of equipment (e.g. hulls, weapons) or for specific items (e.g. ships, tuning kits). These are usually announced eitjher on the Official Battletsar Galactica Online Facebook Page or via the forums on the game's official website. The sale period may be for as little as 1 hour, a whole weekend, or longer. This will normally be included in the announcement.
Sales are often 20% off the particular category of items (though sales of 25% or more have happened on occasion), and (excluding ships) include a discount for upgrading that particluar category of items. Due to in game problems, Ship sales presently do not include a discount for purchasing an advanced ship (e.g. Advanced Mk VII Viper, Advanced War Raider).
It should be noted that if a sale is a 1 hour sale, it will usually coincide with Happy Hour, where you can purchase cubits at a rate of 2 for 1.
As at July 2014, it is not uncommon that (unless a game update is being deployed) there will be 2 x 1 hour sales per week and 1 x weekend long sale in any 7 day period.