The "Max Banners" field represents the total amount of banners you will allow to be sold in that zone, and "Banners" represents how many banners you will display on your site in that zone at one time. This means that if you have 4 total banners available to be sold and 4 displayed at the same time, none will be rotated and each advertiser will get the full amount of impressions that your site gets - not rotated at all.
If you were to change the "Banners" to 1 and keep the "Max Banners" to 4, then there would be 4 banners available that rotate in that 1 spot and they would have to share impressions. (This also means you might need to charge less for the spot since each advertiser's ad is being rotated with 3 other ads and sharing your site's total impressions.)
We also have a tutorial that explains this in more detail: http://buysellads.com/support/help/cat/3/id/366
We tend to answer most support tickets during normal business hours: Monday to Friday, 9:00 am to 6:00 pm (EST). However, we're constantly monitoring tickets, and we'll address urgent issues on nights and weekends, too.Open a Ticket