Hotel attrition clauses can cost you huge penalties if you don't meet your room block requirement. Avoid them if you can by: having a good history of picking up your block; just saying "No" and going elsewhere; taking a smaller block to avoid triggering the clause; or using your overall clout with the hotel chain's national office.
If you can't avoid the attrition clause, minimize your risk by: taking the minimum room block (have exhibitors book directly); increasing room deposit and cancellation requirements; and tying your liability to a defined formula that reflects only room revenue shortfall (the base being average occupancy).
For more on this subject, see the June 5 issue of Tradeshow Week (page 9). This article also includes a clause that you should add to all your hotel contracts. To access, go to www.tradeshowweek.com and click on Article Archives.