When you are doing a deal with a magazine to help promote your show, trade on value, not dollars. This avoids the publisher's argument that "your booth is $3000 and my ad is $9000; therefore, I will give you a 1/3-page ad." The counter argument to this is "the value of your being on our floor for three days in front of 10,000 qualified attendees plus 300 exhibitors exceeds the value of your ad." And deal with the publisher, not the ad sales rep.
Hold your ground. Trade a minimum of a full-page, 4-color ad for a 10x10. In fact, some shows trade three or more ads for a booth, depending on the show's clout in the industry. And do not provide anything that costs you money, such as custom furniture for their booth.
Try for a total relationship with the magazine that provides you multiple ad placements plus access to their subscriber list. More on this in the book.